Localise the UI into Russian and English, switchable without a restart

Strings move into Localization/Strings.resx plus a Russian satellite. XAML uses
a {l:Loc Key} markup extension that yields a binding through the localizer's
indexer rather than a resolved string, so changing the language raises
PropertyChanged for the indexer and every caption in the app re-reads at once.
Resolving strings once at load would have been simpler and would have needed an
app restart to take effect.

Three places where this is more than a string swap:

Russian has three plural forms, so counted messages are assembled from .One /
.Few / .Many keys via Localizer.Plural instead of "{0} records" with an English
plural glued on. "1 запись", "3 записи", "7 записей".

Enum captions in pickers go through LocalizedOption<T>. A value converter would
resolve the caption once and never notice a language change; the wrapper keeps
identity on the enum value so the selection survives, while the label follows
the localizer. It needed a non-generic base for DataTemplate x:DataType, since
Avalonia 12 compiles bindings by default and cannot infer one for an open
generic.

Text originating in the domain would otherwise have stayed English under a
Russian UI — the screenshots showed exactly that. AvParser.Core still knows
nothing about languages: ParseError now carries a Code and Arguments, and the UI
translates Parse.Error.{Code} with a fallback to the English message. Parser
names work the same way (Parser.{id}.Name falling back to DisplayName), which
keeps "add a parser = one registration line" true — an untranslated parser shows
its own name rather than a missing-key marker.

Both .resx files are generated from one table so a key cannot exist in one and
be missing from the other, and the tests assert that, plus no blank translations
and identical {0} placeholder sets — a translation that drops a placeholder
throws at runtime rather than merely reading oddly. A headless test switches
language on a live shell and asserts the rendered text changes without the tree
being rebuilt.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.csharpierignore

@@ -0,0 +1,3 @@
+# Generated from a single source table (see the localization section of CLAUDE.md); reformatting
+# them by hand only creates diff noise.
+**/Localization/Strings*.resx

CLAUDE.md

@@ -107,6 +107,26 @@ dotnet csharpier check .
   значит карантинить здоровые прокси на каждый Cancel.
 - **`Select` и `Next` — зарезервированные слова для CA1716.** Метод стратегии называется `Pick`.
 
+## Добавить строку в UI
+
+1. Ключ и оба перевода — в `Strings.resx` и `Strings.ru.resx` (**оба**, иначе упадёт
+   `LocalizationTests.Russian_translates_every_english_key`).
+2. В XAML — `{l:Loc Ключ}`, во ViewModel — `Localizer.Instance[...]` / `.Format(...)`.
+
+Никакого хардкода в `Views/` кроме имени продукта и примеров адресов.
+
+- **Счётчики — только через `Localizer.Plural`** с ключами `.One` / `.Few` / `.Many`. У русского
+  три формы; «{0} records» с приклеенным окончанием непереводимо.
+- **Перечисления в списках — `LocalizedOption<T>`**, не сырые значения. Конвертер разрешил бы
+  подпись один раз и не заметил смены языка. Идентичность обёртки — значение перечисления, чтобы
+  выбор не слетал.
+- **Текст из домена переводится по коду.** `Core` о языках не знает: `ParseError` несёт `Code` и
+  `Arguments`, UI ищет `Parse.Error.{Code}` с откатом на `Message`. Имена парсеров — так же:
+  `Parser.{id}.Name` с откатом на `DisplayName`, поэтому обещание «добавить парсер = одна строка»
+  остаётся в силе.
+- **VM, у которой есть производный от языка текст, переопределяет `OnLanguageChanged`** и зовёт
+  `base`. Без этого заголовок страницы останется на прежнем языке.
+
 ## Грабли, уже оплаченные
 
 - **Селектор типа в Avalonia матчит точный тип.** `UserControl.shell` не матчит `ShellView`

README.md

@@ -152,6 +152,41 @@ using (lease)
 SOCKS работает штатно: .NET понимает схемы `socks4/socks4a/socks5` в `WebProxy`. Учтите, что
 proxifly-запись с `"protocol": "https"` — это всё равно HTTP-прокси с CONNECT, а не схема `https://`.
 
+## Локализация
+
+Русский и английский, переключение **без перезапуска** — язык выбирается в настройках
+(«Системный» берёт язык ОС, если для него есть перевод, иначе английский).
+
+Строки лежат в `UI/Localization/Strings.resx` и `Strings.ru.resx`; русский собирается в
+сателлитную сборку `ru/AvParser.UI.resources.dll`.
+
+В XAML — разметочное расширение:
+
+```xml
+<TextBlock Text="{l:Loc Parse.Run}" />
+```
+
+Оно возвращает **биндинг** через индексатор `Localizer`, а не готовую строку: смена языка
+поднимает `PropertyChanged` для индексатора, и все такие биндинги перечитываются разом. Строка,
+разрешённая один раз при загрузке, потребовала бы перезапуска.
+
+Три места, где локализация упирается в грамматику или в слои:
+
+- **Множественные числа.** У русского три формы, поэтому счётчики собираются не из «{0} records»
+  с приклеенным окончанием, а из ключей `.One` / `.Few` / `.Many` через `Localizer.Plural`.
+  «1 запись», «3 записи», «7 записей».
+- **Значения перечислений.** Конвертер разрешил бы подпись один раз и не заметил смены языка,
+  поэтому в списках лежат обёртки `LocalizedOption<T>`: идентичность — значение перечисления
+  (выбор не слетает), подпись следует за локализатором.
+- **Текст из домена.** `AvParser.Core` о языках не знает. Парсеры отдают английское сообщение
+  **и код**, а UI переводит `Parse.Error.{Code}` с откатом на сообщение. Так же и с именами
+  парсеров: `Parser.{id}.Name` с откатом на `DisplayName`, поэтому новый парсер работает
+  непереведённым, а не показывает `!ключ!`.
+
+Оба `.resx` генерируются из одной таблицы, чтобы ключ не мог существовать в одном файле и
+отсутствовать в другом; тесты проверяют совпадение ключей, отсутствие пустых переводов и
+одинаковый набор плейсхолдеров `{0}`.
+
 ## Дизайн-токены
 
 Все цвета, отступы, радиусы и типографика — в `Styles/Tokens.axaml`, с отдельными словарями

src/AvParser.Core/Parsing/ParseError.cs

@@ -5,6 +5,25 @@ namespace AvParser.Core.Parsing;
 /// <param name="Message">What went wrong, phrased for a user rather than a developer.</param>
 public sealed record ParseError(int LineNumber, string Message)
 {
+    /// <summary>
+    /// Stable identifier for the kind of failure, or <see langword="null"/> when the message is
+    /// the only thing on offer.
+    /// </summary>
+    /// <remarks>
+    /// The domain stays language-free: it produces an English message plus a code, and the UI
+    /// translates <c>Parse.Error.{Code}</c> with <see cref="Arguments"/>, falling back to
+    /// <see cref="Message"/>. Without this, a Russian UI would still print English error text —
+    /// and moving the strings themselves into the domain would drag localisation down there.
+    /// </remarks>
+    public string? Code { get; init; }
+
+    /// <summary>Values to substitute into the translated message.</summary>
+    public IReadOnlyList<object?> Arguments { get; init; } = [];
+
+    /// <summary>Creates an error carrying a translation code.</summary>
+    public static ParseError Create(int lineNumber, string code, string message, params object?[] arguments) =>
+        new(lineNumber, message) { Code = code, Arguments = arguments };
+
     /// <inheritdoc />
     public override string ToString() => $"Line {LineNumber}: {Message}";
 }

src/AvParser.Core/Parsing/ParseOutcome.cs

@@ -37,4 +37,8 @@ public readonly record struct ParseOutcome<T>
     /// <summary>Creates a failed outcome from its parts.</summary>
     public static ParseOutcome<T> Failure(int lineNumber, string message) =>
         Failure(new ParseError(lineNumber, message));
+
+    /// <summary>Creates a failed outcome carrying a translation code.</summary>
+    public static ParseOutcome<T> Failure(int lineNumber, string code, string message, params object?[] arguments) =>
+        Failure(ParseError.Create(lineNumber, code, message, arguments));
 }

src/AvParser.Core/Parsing/Samples/DelimitedTextParser.cs

@@ -69,7 +69,10 @@ public sealed class DelimitedTextParser : ITextParser
             {
                 yield return ParseOutcome<ParsedRecord>.Failure(
                     lineNumber,
-                    $"Expected {header.Length} field(s) but found {values.Length}."
+                    "FieldCount",
+                    $"Expected {header.Length} field(s) but found {values.Length}.",
+                    header.Length,
+                    values.Length
                 );
             }
             else
@@ -93,7 +96,7 @@ public sealed class DelimitedTextParser : ITextParser
 
         if (header is null)
         {
-            yield return ParseOutcome<ParsedRecord>.Failure(1, "Input contains no header row.");
+            yield return ParseOutcome<ParsedRecord>.Failure(1, "NoHeader", "Input contains no header row.");
         }
 
         progress?.Report(new ParseProgress(total, total));

src/AvParser.Core/Parsing/Samples/KeyValueTextParser.cs

@@ -51,7 +51,11 @@ public sealed class KeyValueTextParser : ITextParser
 
                 if (separatorIndex <= 0)
                 {
-                    yield return ParseOutcome<ParsedRecord>.Failure(lineNumber, "No '=' or ':' separator found.");
+                    yield return ParseOutcome<ParsedRecord>.Failure(
+                        lineNumber,
+                        "NoSeparator",
+                        "No '=' or ':' separator found."
+                    );
                 }
                 else
                 {
@@ -59,7 +63,7 @@ public sealed class KeyValueTextParser : ITextParser
                     var value = line[(separatorIndex + 1)..].Trim();
 
                     yield return key.Length == 0
-                        ? ParseOutcome<ParsedRecord>.Failure(lineNumber, "Key is empty.")
+                        ? ParseOutcome<ParsedRecord>.Failure(lineNumber, "EmptyKey", "Key is empty.")
                         : ParseOutcome<ParsedRecord>.Success(
                             new ParsedRecord(lineNumber, [new ParsedField("Key", key), new ParsedField("Value", value)])
                         );

src/AvParser.Core/Settings/AppLanguage.cs

@@ -0,0 +1,45 @@
+using System.Globalization;
+
+namespace AvParser.Core.Settings;
+
+/// <summary>UI language. <see cref="System"/> follows the operating system.</summary>
+public enum AppLanguage
+{
+    /// <summary>Follow the operating system, falling back to English.</summary>
+    System = 0,
+
+    /// <summary>English.</summary>
+    English = 1,
+
+    /// <summary>Russian.</summary>
+    Russian = 2,
+}
+
+/// <summary>Maps <see cref="AppLanguage"/> onto cultures.</summary>
+public static class AppLanguages
+{
+    /// <summary>Languages the app ships translations for.</summary>
+    public static IReadOnlyList<AppLanguage> All { get; } =
+    [AppLanguage.System, AppLanguage.English, AppLanguage.Russian];
+
+    /// <summary>
+    /// Resolves a language to the culture the resource lookup should use.
+    /// </summary>
+    /// <remarks>
+    /// <see cref="AppLanguage.System"/> resolves to Russian only when the OS is actually Russian;
+    /// anything else lands on English, because those are the two translations that exist and a
+    /// half-translated German would be worse than plain English.
+    /// </remarks>
+    public static CultureInfo ToCulture(AppLanguage language, CultureInfo? systemCulture = null) =>
+        language switch
+        {
+            AppLanguage.English => CultureInfo.GetCultureInfo("en"),
+            AppLanguage.Russian => CultureInfo.GetCultureInfo("ru"),
+            _ => FromSystem(systemCulture ?? CultureInfo.CurrentUICulture),
+        };
+
+    private static CultureInfo FromSystem(CultureInfo culture) =>
+        string.Equals(culture.TwoLetterISOLanguageName, "ru", StringComparison.OrdinalIgnoreCase)
+            ? CultureInfo.GetCultureInfo("ru")
+            : CultureInfo.GetCultureInfo("en");
+}

src/AvParser.Core/Settings/AppSettings.cs

@@ -27,6 +27,9 @@ public sealed record AppSettings
     /// <summary>Chosen theme variant.</summary>
     public AppTheme Theme { get; init; } = AppTheme.System;
 
+    /// <summary>Chosen UI language.</summary>
+    public AppLanguage Language { get; init; } = AppLanguage.System;
+
     /// <summary>Id of the parser selected last time; resolved leniently on load.</summary>
     public string? LastParserId { get; init; }
 

src/AvParser.Desktop/App.axaml.cs

@@ -43,7 +43,9 @@ public partial class App : Application
 
         DataTemplates.Add(_services.GetRequiredService<ViewLocator>());
 
-        // Resolving the theme service applies the persisted variant as a side effect of construction.
+        // Both of these apply the persisted choice as a side effect of construction, so they have
+        // to be resolved before the first window is built rather than lazily on the Settings page.
+        _ = _services.GetRequiredService<ILocalizationService>();
         _ = _services.GetRequiredService<IThemeService>();
 
         if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)

src/AvParser.UI/AvParser.UI.csproj

@@ -10,6 +10,14 @@
     <AvaloniaResource Include="Assets\**" />
   </ItemGroup>
 
+  <ItemGroup>
+    <!-- No designer class: strings are reached through Localizer's indexer so that bindings can
+         re-read them when the language changes. A generated static accessor would be resolved
+         once and would need an app restart to take effect. -->
+    <EmbeddedResource Update="Localization\Strings.resx" Generator="" />
+    <EmbeddedResource Update="Localization\Strings.ru.resx" Generator="" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\AvParser.Core\AvParser.Core.csproj" />
     <ProjectReference Include="..\AvParser.Infrastructure\AvParser.Infrastructure.csproj" />

src/AvParser.UI/DependencyInjection/UiServiceCollectionExtensions.cs

@@ -26,6 +26,7 @@ public static class UiServiceCollectionExtensions
 
         services.AddSingleton<ViewLocator>();
         services.AddSingleton<IThemeService, ThemeService>();
+        services.AddSingleton<ILocalizationService, LocalizationService>();
         services.AddSingleton<INavigationService, NavigationService>();
 
         services.AddSingleton<DashboardViewModel>();
@@ -39,7 +40,8 @@ public static class UiServiceCollectionExtensions
             sp.GetRequiredService<IThemeService>(),
             sp.GetRequiredService<IAppPaths>(),
             sp.GetRequiredService<LoggingLevelSwitch>(),
-            sp.GetRequiredService<IProxyPool>()
+            sp.GetRequiredService<IProxyPool>(),
+            sp.GetRequiredService<ILocalizationService>()
         ));
         services.AddSingleton<ProxiesViewModel>(static sp => new ProxiesViewModel(
             sp.GetRequiredService<IProxyPool>(),

src/AvParser.UI/Localization/LocExtension.cs

@@ -0,0 +1,33 @@
+using Avalonia.Data;
+using Avalonia.Markup.Xaml;
+
+namespace AvParser.UI.Localization;
+
+/// <summary>
+/// XAML shorthand for a translated string: <c>Text="{l:Loc Parse.Title}"</c>.
+/// </summary>
+/// <remarks>
+/// Returns a <see cref="Binding"/> through <see cref="Localizer"/>'s indexer rather than the
+/// string itself. A plain string would be resolved once at load and would never notice a language
+/// change; the binding re-reads when the localizer invalidates its indexer.
+/// </remarks>
+public sealed class LocExtension : MarkupExtension
+{
+    /// <summary>Creates the extension with no key. Used by XAML before the key is assigned.</summary>
+    public LocExtension() => Key = string.Empty;
+
+    /// <summary>Creates the extension for a resource key.</summary>
+    public LocExtension(string key) => Key = key;
+
+    /// <summary>Resource key to look up.</summary>
+    public string Key { get; set; }
+
+    /// <inheritdoc />
+    public override object ProvideValue(IServiceProvider serviceProvider) =>
+        new Binding
+        {
+            Mode = BindingMode.OneWay,
+            Source = Localizer.Instance,
+            Path = $"[{Key}]",
+        };
+}

src/AvParser.UI/Localization/LocalizedOption.cs

@@ -0,0 +1,66 @@
+using ReactiveUI;
+
+namespace AvParser.UI.Localization;
+
+/// <summary>
+/// An enum value paired with its translated label, for pickers.
+/// </summary>
+/// <remarks>
+/// Combo boxes cannot bind a raw enum to a translated caption: a value converter would resolve the
+/// text once and never notice a language change. Wrapping the value keeps the selection stable
+/// (identity is the enum value) while the label follows the localizer.
+/// </remarks>
+public abstract class LocalizedOption : ReactiveObject
+{
+    /// <summary>Translated caption.</summary>
+    /// <remarks>
+    /// Declared on a non-generic base so a <c>DataTemplate</c> can name a concrete
+    /// <c>x:DataType</c>: Avalonia 12 compiles bindings by default and cannot infer one for an
+    /// open generic.
+    /// </remarks>
+    public abstract string Label { get; }
+}
+
+/// <inheritdoc cref="LocalizedOption" />
+public sealed class LocalizedOption<TValue> : LocalizedOption, IEquatable<LocalizedOption<TValue>>
+    where TValue : struct, Enum
+{
+    private readonly string _key;
+
+    /// <summary>Creates an option for a value, reading its label from <c>Enum.{Type}.{Value}</c>.</summary>
+    public LocalizedOption(TValue value)
+    {
+        Value = value;
+        _key = $"Enum.{typeof(TValue).Name}.{value}";
+
+        Localizer.Instance.LanguageChanged += OnLanguageChanged;
+    }
+
+    /// <summary>The underlying value.</summary>
+    public TValue Value { get; }
+
+    /// <inheritdoc />
+    public override string Label => Localizer.Instance[_key];
+
+    /// <summary>Builds options for every value of the enum.</summary>
+    public static IReadOnlyList<LocalizedOption<TValue>> ForAll() =>
+        [.. Enum.GetValues<TValue>().Select(value => new LocalizedOption<TValue>(value))];
+
+    /// <summary>Builds options for a specific set of values, in that order.</summary>
+    public static IReadOnlyList<LocalizedOption<TValue>> For(params TValue[] values) =>
+        [.. values.Select(value => new LocalizedOption<TValue>(value))];
+
+    /// <inheritdoc />
+    public bool Equals(LocalizedOption<TValue>? other) => other is not null && Value.Equals(other.Value);
+
+    /// <inheritdoc />
+    public override bool Equals(object? obj) => Equals(obj as LocalizedOption<TValue>);
+
+    /// <inheritdoc />
+    public override int GetHashCode() => Value.GetHashCode();
+
+    /// <inheritdoc />
+    public override string ToString() => Label;
+
+    private void OnLanguageChanged(object? sender, EventArgs e) => this.RaisePropertyChanged(nameof(Label));
+}

src/AvParser.UI/Localization/Localizer.cs

@@ -0,0 +1,137 @@
+using System.ComponentModel;
+using System.Globalization;
+using System.Resources;
+using AvParser.Core.Settings;
+
+namespace AvParser.UI.Localization;
+
+/// <summary>
+/// The single source of translated strings, and the thing bindings listen to.
+/// </summary>
+/// <remarks>
+/// <para>
+/// Exposed as an indexer so XAML can bind through it: changing the language raises
+/// <c>PropertyChanged</c> for the indexer, which makes every
+/// <c>{l:Loc Key}</c> binding in the application re-read at once. That is what buys language
+/// switching without a restart — the alternative, resolving strings once at load, would need one.
+/// </para>
+/// <para>
+/// A singleton rather than an injected service because XAML markup extensions have no container
+/// to ask, and a second instance would simply be a second set of stale bindings.
+/// </para>
+/// </remarks>
+public sealed class Localizer : INotifyPropertyChanged
+{
+    /// <summary>WPF/Avalonia convention: this property name invalidates every indexer binding.</summary>
+    private const string IndexerName = "Item[]";
+
+    private static readonly ResourceManager Resources = new(
+        "AvParser.UI.Localization.Strings",
+        typeof(Localizer).Assembly
+    );
+
+    private CultureInfo _culture = CultureInfo.GetCultureInfo("en");
+
+    private Localizer() { }
+
+    /// <summary>The instance every binding goes through.</summary>
+    public static Localizer Instance { get; } = new();
+
+    /// <summary>Culture currently used for lookups.</summary>
+    public CultureInfo Culture => _culture;
+
+    /// <summary>The language setting currently applied.</summary>
+    public AppLanguage Language { get; private set; } = AppLanguage.System;
+
+    /// <inheritdoc />
+    public event PropertyChangedEventHandler? PropertyChanged;
+
+    /// <summary>Raised after the language changes, for consumers that cache derived text.</summary>
+    public event EventHandler? LanguageChanged;
+
+    /// <summary>Looks a key up. Unknown keys come back as <c>!key!</c> rather than blank.</summary>
+    /// <remarks>
+    /// A visible marker beats an empty label: a missing translation should be obvious in a
+    /// screenshot, not silently render as nothing.
+    /// </remarks>
+    public string this[string key] => Get(key);
+
+    /// <summary>Looks a key up.</summary>
+    public string Get(string key)
+    {
+        if (string.IsNullOrEmpty(key))
+        {
+            return string.Empty;
+        }
+
+        return Resources.GetString(key, _culture) ?? $"!{key}!";
+    }
+
+    /// <summary>Looks a key up, returning <paramref name="fallback"/> when it is not translated.</summary>
+    /// <remarks>
+    /// Used for text that plugs into the app from outside the resource files — a newly added
+    /// parser should show its own English name rather than <c>!Parser.x.Name!</c> until someone
+    /// gets round to translating it.
+    /// </remarks>
+    public string GetOrDefault(string key, string fallback) => Resources.GetString(key, _culture) ?? fallback;
+
+    /// <summary>Looks a key up and formats it with <paramref name="arguments"/>.</summary>
+    public string Format(string key, params object?[] arguments) => string.Format(_culture, Get(key), arguments);
+
+    /// <summary>
+    /// Picks the plural form of <paramref name="key"/> for <paramref name="count"/> and formats it.
+    /// </summary>
+    /// <remarks>
+    /// Resource keys are suffixed <c>.One</c> / <c>.Few</c> / <c>.Many</c>. English only ever
+    /// needs One and Many; Russian needs all three, which is why the counted messages cannot just
+    /// be "{0} records" with an English-shaped plural glued on.
+    /// </remarks>
+    public string Plural(string key, int count) =>
+        string.Format(_culture, Get($"{key}.{SuffixFor(count, _culture)}"), count);
+
+    /// <summary>Applies a language and notifies every binding.</summary>
+    public void SetLanguage(AppLanguage language, CultureInfo? systemCulture = null)
+    {
+        var culture = AppLanguages.ToCulture(language, systemCulture);
+        var changed = !Equals(culture, _culture) || language != Language;
+
+        _culture = culture;
+        Language = language;
+
+        if (!changed)
+        {
+            return;
+        }
+
+        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(IndexerName));
+        LanguageChanged?.Invoke(this, EventArgs.Empty);
+    }
+
+    /// <summary>Chooses the plural suffix for a count under a culture.</summary>
+    /// <remarks>Public so the rules can be tested directly rather than through resource lookups.</remarks>
+    public static string SuffixFor(int count, CultureInfo culture)
+    {
+        ArgumentNullException.ThrowIfNull(culture);
+
+        if (!string.Equals(culture.TwoLetterISOLanguageName, "ru", StringComparison.OrdinalIgnoreCase))
+        {
+            return count == 1 ? "One" : "Many";
+        }
+
+        var absolute = Math.Abs(count);
+        var lastTwo = absolute % 100;
+        var last = absolute % 10;
+
+        if (lastTwo is >= 11 and <= 14)
+        {
+            return "Many";
+        }
+
+        return last switch
+        {
+            1 => "One",
+            2 or 3 or 4 => "Few",
+            _ => "Many",
+        };
+    }
+}

src/AvParser.UI/Localization/Strings.resx

@@ -0,0 +1,490 @@
+<?xml version="1.0" encoding="utf-8"?>
+<root>
+  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
+    <xsd:import namespace="http://www.w3.org/XML/1998/namespace" />
+    <xsd:element name="root" msdata:IsDataSet="true">
+      <xsd:complexType>
+        <xsd:choice maxOccurs="unbounded">
+          <xsd:element name="metadata">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" />
+              </xsd:sequence>
+              <xsd:attribute name="name" use="required" type="xsd:string" />
+              <xsd:attribute name="type" type="xsd:string" />
+              <xsd:attribute name="mimetype" type="xsd:string" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="assembly">
+            <xsd:complexType>
+              <xsd:attribute name="alias" type="xsd:string" />
+              <xsd:attribute name="name" type="xsd:string" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="data">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+                <xsd:element name="comment" type="xsd:string" minOccurs="0" msdata:Ordinal="2" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" msdata:Ordinal="1" />
+              <xsd:attribute name="type" type="xsd:string" msdata:Ordinal="3" />
+              <xsd:attribute name="mimetype" type="xsd:string" msdata:Ordinal="4" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="resheader">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" />
+            </xsd:complexType>
+          </xsd:element>
+        </xsd:choice>
+      </xsd:complexType>
+    </xsd:element>
+  </xsd:schema>
+  <resheader name="resmimetype">
+    <value>text/microsoft-resx</value>
+  </resheader>
+  <resheader name="version">
+    <value>2.0</value>
+  </resheader>
+  <resheader name="reader">
+    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <resheader name="writer">
+    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <data name="Shell.ToggleNavigation" xml:space="preserve">
+    <value>Toggle navigation</value>
+  </data>
+  <data name="Shell.Back" xml:space="preserve">
+    <value>Back</value>
+  </data>
+  <data name="Shell.ToggleTheme" xml:space="preserve">
+    <value>Switch light / dark</value>
+  </data>
+  <data name="Page.Dashboard" xml:space="preserve">
+    <value>Dashboard</value>
+  </data>
+  <data name="Page.Parse" xml:space="preserve">
+    <value>Parse</value>
+  </data>
+  <data name="Page.Proxies" xml:space="preserve">
+    <value>Proxies</value>
+  </data>
+  <data name="Page.Settings" xml:space="preserve">
+    <value>Settings</value>
+  </data>
+  <data name="Page.About" xml:space="preserve">
+    <value>About</value>
+  </data>
+  <data name="Dashboard.Tagline" xml:space="preserve">
+    <value>A parser shell with an adaptive layout. Drag the window narrower to watch the navigation collapse to an icon rail and then to an overlay drawer.</value>
+  </data>
+  <data name="Dashboard.RegisteredParsers" xml:space="preserve">
+    <value>Registered parsers</value>
+  </data>
+  <data name="Dashboard.GetStarted" xml:space="preserve">
+    <value>Get started</value>
+  </data>
+  <data name="Dashboard.OpenParser" xml:space="preserve">
+    <value>Open the parser</value>
+  </data>
+  <data name="Dashboard.DataDirectory" xml:space="preserve">
+    <value>DATA DIRECTORY</value>
+  </data>
+  <data name="Parse.Parser" xml:space="preserve">
+    <value>PARSER</value>
+  </data>
+  <data name="Parse.Actions" xml:space="preserve">
+    <value>ACTIONS</value>
+  </data>
+  <data name="Parse.Run" xml:space="preserve">
+    <value>Parse</value>
+  </data>
+  <data name="Parse.Cancel" xml:space="preserve">
+    <value>Cancel</value>
+  </data>
+  <data name="Parse.Sample" xml:space="preserve">
+    <value>Sample</value>
+  </data>
+  <data name="Parse.SampleTip" xml:space="preserve">
+    <value>Fill the input with a small example</value>
+  </data>
+  <data name="Parse.LargeSample" xml:space="preserve">
+    <value>50k rows</value>
+  </data>
+  <data name="Parse.LargeSampleTip" xml:space="preserve">
+    <value>Generate 50 000 rows, so progress and cancellation are observable</value>
+  </data>
+  <data name="Parse.ClearTip" xml:space="preserve">
+    <value>Clear input and results</value>
+  </data>
+  <data name="Parse.Input" xml:space="preserve">
+    <value>INPUT</value>
+  </data>
+  <data name="Parse.InputPlaceholder" xml:space="preserve">
+    <value>Paste text here, or press Sample</value>
+  </data>
+  <data name="Parse.Records" xml:space="preserve">
+    <value>RECORDS</value>
+  </data>
+  <data name="Parse.Errors" xml:space="preserve">
+    <value>ERRORS</value>
+  </data>
+  <data name="Parse.Count.Records.One" xml:space="preserve">
+    <value>{0} record</value>
+  </data>
+  <data name="Parse.Count.Records.Few" xml:space="preserve">
+    <value>{0} records</value>
+  </data>
+  <data name="Parse.Count.Records.Many" xml:space="preserve">
+    <value>{0} records</value>
+  </data>
+  <data name="Parse.Count.Errors.One" xml:space="preserve">
+    <value>{0} error</value>
+  </data>
+  <data name="Parse.Count.Errors.Few" xml:space="preserve">
+    <value>{0} errors</value>
+  </data>
+  <data name="Parse.Count.Errors.Many" xml:space="preserve">
+    <value>{0} errors</value>
+  </data>
+  <data name="Parse.Status.Done" xml:space="preserve">
+    <value>Parsed {0} in {1} ms.</value>
+  </data>
+  <data name="Parse.Status.Cancelled" xml:space="preserve">
+    <value>Cancelled after {0} in {1} ms.</value>
+  </data>
+  <data name="Parse.Status.WithErrors" xml:space="preserve">
+    <value>{0}, {1}.</value>
+  </data>
+  <data name="Parse.Status.Truncated" xml:space="preserve">
+    <value>Showing the first {0} only.</value>
+  </data>
+  <data name="Parse.Status.Failed" xml:space="preserve">
+    <value>Parse failed: {0}</value>
+  </data>
+  <data name="Proxies.Pool" xml:space="preserve">
+    <value>POOL</value>
+  </data>
+  <data name="Proxies.Refresh" xml:space="preserve">
+    <value>Refresh</value>
+  </data>
+  <data name="Proxies.RefreshTip" xml:space="preserve">
+    <value>Reload every source</value>
+  </data>
+  <data name="Proxies.CheckAll" xml:space="preserve">
+    <value>Check all</value>
+  </data>
+  <data name="Proxies.CheckAllTip" xml:space="preserve">
+    <value>Probe every proxy in the pool</value>
+  </data>
+  <data name="Proxies.Search" xml:space="preserve">
+    <value>SEARCH</value>
+  </data>
+  <data name="Proxies.SearchPlaceholder" xml:space="preserve">
+    <value>address or country</value>
+  </data>
+  <data name="Proxies.Protocol" xml:space="preserve">
+    <value>PROTOCOL</value>
+  </data>
+  <data name="Proxies.StatusColumn" xml:space="preserve">
+    <value>STATUS</value>
+  </data>
+  <data name="Proxies.Alive" xml:space="preserve">
+    <value>alive</value>
+  </data>
+  <data name="Proxies.Total" xml:space="preserve">
+    <value>total</value>
+  </data>
+  <data name="Proxies.Matched" xml:space="preserve">
+    <value>matched</value>
+  </data>
+  <data name="Proxies.ListHeader" xml:space="preserve">
+    <value>PROXIES</value>
+  </data>
+  <data name="Proxies.CustomHeader" xml:space="preserve">
+    <value>CUSTOM PROXIES</value>
+  </data>
+  <data name="Proxies.Add" xml:space="preserve">
+    <value>Add</value>
+  </data>
+  <data name="Proxies.Remove" xml:space="preserve">
+    <value>Remove</value>
+  </data>
+  <data name="Proxies.RemoveTip" xml:space="preserve">
+    <value>Remove the selected custom proxy</value>
+  </data>
+  <data name="Proxies.ClearTip" xml:space="preserve">
+    <value>Clear the custom list</value>
+  </data>
+  <data name="Proxies.CustomHint" xml:space="preserve">
+    <value>One per line. scheme://host:port, or host:port for plain HTTP. user:pass@ is supported.</value>
+  </data>
+  <data name="Proxies.Health.Alive" xml:space="preserve">
+    <value>alive</value>
+  </data>
+  <data name="Proxies.Health.Dead" xml:space="preserve">
+    <value>dead</value>
+  </data>
+  <data name="Proxies.Health.Unchecked" xml:space="preserve">
+    <value>unchecked</value>
+  </data>
+  <data name="Proxies.Source.Feed" xml:space="preserve">
+    <value>feed</value>
+  </data>
+  <data name="Proxies.Source.Custom" xml:space="preserve">
+    <value>custom</value>
+  </data>
+  <data name="Proxies.Count.Proxies.One" xml:space="preserve">
+    <value>{0} proxy</value>
+  </data>
+  <data name="Proxies.Count.Proxies.Few" xml:space="preserve">
+    <value>{0} proxies</value>
+  </data>
+  <data name="Proxies.Count.Proxies.Many" xml:space="preserve">
+    <value>{0} proxies</value>
+  </data>
+  <data name="Proxies.Status.PoolHolds" xml:space="preserve">
+    <value>Pool holds {0}.</value>
+  </data>
+  <data name="Proxies.Status.Nothing" xml:space="preserve">
+    <value>Nothing to add.</value>
+  </data>
+  <data name="Proxies.Status.Added" xml:space="preserve">
+    <value>Added {0} of {1}.</value>
+  </data>
+  <data name="Proxies.Status.Rejected" xml:space="preserve">
+    <value>Could not parse: {0}</value>
+  </data>
+  <data name="Proxies.Status.RejectedMore" xml:space="preserve">
+    <value>and {0} more</value>
+  </data>
+  <data name="Proxies.Status.Answered" xml:space="preserve">
+    <value>{0} of {1} answered.</value>
+  </data>
+  <data name="Proxies.Status.CheckCancelled" xml:space="preserve">
+    <value>Check cancelled.</value>
+  </data>
+  <data name="Proxies.Status.Removed" xml:space="preserve">
+    <value>Removed {0}.</value>
+  </data>
+  <data name="Proxies.Status.Cleared" xml:space="preserve">
+    <value>Custom list cleared.</value>
+  </data>
+  <data name="Proxies.Status.Failed" xml:space="preserve">
+    <value>Failed: {0}</value>
+  </data>
+  <data name="Settings.Appearance" xml:space="preserve">
+    <value>Appearance</value>
+  </data>
+  <data name="Settings.Theme" xml:space="preserve">
+    <value>THEME</value>
+  </data>
+  <data name="Settings.ThemeHint" xml:space="preserve">
+    <value>System follows the operating system's light/dark setting.</value>
+  </data>
+  <data name="Settings.Language" xml:space="preserve">
+    <value>LANGUAGE</value>
+  </data>
+  <data name="Settings.LanguageHint" xml:space="preserve">
+    <value>Applies immediately — no restart needed.</value>
+  </data>
+  <data name="Settings.Diagnostics" xml:space="preserve">
+    <value>Diagnostics</value>
+  </data>
+  <data name="Settings.LogLevel" xml:space="preserve">
+    <value>MINIMUM LOG LEVEL</value>
+  </data>
+  <data name="Settings.LogLevelHint" xml:space="preserve">
+    <value>Applies immediately — no restart needed.</value>
+  </data>
+  <data name="Settings.SettingsFile" xml:space="preserve">
+    <value>SETTINGS FILE</value>
+  </data>
+  <data name="Settings.LogDirectory" xml:space="preserve">
+    <value>LOG DIRECTORY</value>
+  </data>
+  <data name="Settings.Proxies" xml:space="preserve">
+    <value>Proxies</value>
+  </data>
+  <data name="Settings.Rotation" xml:space="preserve">
+    <value>ROTATION</value>
+  </data>
+  <data name="Settings.LivenessCheck" xml:space="preserve">
+    <value>LIVENESS CHECK</value>
+  </data>
+  <data name="Settings.UseFeed" xml:space="preserve">
+    <value>Use the public proxifly feed</value>
+  </data>
+  <data name="Settings.ProbeUrl" xml:space="preserve">
+    <value>PROBE URL</value>
+  </data>
+  <data name="Settings.ProbeUrlHint" xml:space="preserve">
+    <value>Plain HTTP by default: requiring TLS would fail every proxy that cannot do CONNECT, not just the dead ones.</value>
+  </data>
+  <data name="Settings.ProbeTimeout" xml:space="preserve">
+    <value>PROBE TIMEOUT (SEC)</value>
+  </data>
+  <data name="Settings.ProbeConcurrency" xml:space="preserve">
+    <value>PARALLEL PROBES</value>
+  </data>
+  <data name="Settings.Rotation.Sticky" xml:space="preserve">
+    <value>One proxy per session, replaced only when it fails. Keeps site sessions intact.</value>
+  </data>
+  <data name="Settings.Rotation.RoundRobin" xml:space="preserve">
+    <value>A different proxy on every request. Spreads rate limits, but breaks session cookies.</value>
+  </data>
+  <data name="Settings.Rotation.WeightedRandom" xml:space="preserve">
+    <value>Random, weighted by feed score and how often the proxy has actually worked here.</value>
+  </data>
+  <data name="Settings.HealthCheck.Pool" xml:space="preserve">
+    <value>Probe the whole pool up front, in parallel. One sweep, then no per-request delay.</value>
+  </data>
+  <data name="Settings.HealthCheck.Lazy" xml:space="preserve">
+    <value>Probe each proxy as it is handed out. No sweep, but every acquisition pays a round trip.</value>
+  </data>
+  <data name="Settings.Breakpoints" xml:space="preserve">
+    <value>Layout breakpoints</value>
+  </data>
+  <data name="Settings.BreakpointsHint" xml:space="preserve">
+    <value>Window widths at which the navigation changes shape. Resize the window to see it happen.</value>
+  </data>
+  <data name="Settings.Breakpoint.Compact" xml:space="preserve">
+    <value>COMPACT</value>
+  </data>
+  <data name="Settings.Breakpoint.Medium" xml:space="preserve">
+    <value>MEDIUM</value>
+  </data>
+  <data name="Settings.Breakpoint.Expanded" xml:space="preserve">
+    <value>EXPANDED</value>
+  </data>
+  <data name="Settings.Breakpoint.CompactHint" xml:space="preserve">
+    <value>below {0} px — overlay drawer</value>
+  </data>
+  <data name="Settings.Breakpoint.MediumHint" xml:space="preserve">
+    <value>{0} – {1} px — icon rail</value>
+  </data>
+  <data name="Settings.Breakpoint.ExpandedHint" xml:space="preserve">
+    <value>from {0} px — full sidebar</value>
+  </data>
+  <data name="About.BuiltWith" xml:space="preserve">
+    <value>Built with</value>
+  </data>
+  <data name="About.OnDisk" xml:space="preserve">
+    <value>On disk</value>
+  </data>
+  <data name="About.Data" xml:space="preserve">
+    <value>DATA</value>
+  </data>
+  <data name="About.Logs" xml:space="preserve">
+    <value>LOGS</value>
+  </data>
+  <data name="About.Component.Dotnet" xml:space="preserve">
+    <value>.NET</value>
+  </data>
+  <data name="About.Component.Os" xml:space="preserve">
+    <value>Operating system</value>
+  </data>
+  <data name="About.Component.Avalonia" xml:space="preserve">
+    <value>Avalonia</value>
+  </data>
+  <data name="About.Component.ReactiveUI" xml:space="preserve">
+    <value>ReactiveUI</value>
+  </data>
+  <data name="About.Component.Semi" xml:space="preserve">
+    <value>Semi.Avalonia</value>
+  </data>
+  <data name="About.Component.NotLoaded" xml:space="preserve">
+    <value>not loaded</value>
+  </data>
+  <data name="Enum.AppTheme.System" xml:space="preserve">
+    <value>System</value>
+  </data>
+  <data name="Enum.AppTheme.Light" xml:space="preserve">
+    <value>Light</value>
+  </data>
+  <data name="Enum.AppTheme.Dark" xml:space="preserve">
+    <value>Dark</value>
+  </data>
+  <data name="Enum.AppLanguage.System" xml:space="preserve">
+    <value>System</value>
+  </data>
+  <data name="Enum.AppLanguage.English" xml:space="preserve">
+    <value>English</value>
+  </data>
+  <data name="Enum.AppLanguage.Russian" xml:space="preserve">
+    <value>Русский</value>
+  </data>
+  <data name="Enum.ProxyRotation.Sticky" xml:space="preserve">
+    <value>Sticky</value>
+  </data>
+  <data name="Enum.ProxyRotation.RoundRobin" xml:space="preserve">
+    <value>Round-robin</value>
+  </data>
+  <data name="Enum.ProxyRotation.WeightedRandom" xml:space="preserve">
+    <value>Weighted random</value>
+  </data>
+  <data name="Enum.ProxyHealthCheck.Pool" xml:space="preserve">
+    <value>Whole pool</value>
+  </data>
+  <data name="Enum.ProxyHealthCheck.Lazy" xml:space="preserve">
+    <value>On hand-out</value>
+  </data>
+  <data name="Enum.ProxyProtocolFilter.All" xml:space="preserve">
+    <value>All</value>
+  </data>
+  <data name="Enum.ProxyProtocolFilter.Http" xml:space="preserve">
+    <value>HTTP</value>
+  </data>
+  <data name="Enum.ProxyProtocolFilter.Https" xml:space="preserve">
+    <value>HTTPS</value>
+  </data>
+  <data name="Enum.ProxyProtocolFilter.Socks4" xml:space="preserve">
+    <value>SOCKS4</value>
+  </data>
+  <data name="Enum.ProxyProtocolFilter.Socks5" xml:space="preserve">
+    <value>SOCKS5</value>
+  </data>
+  <data name="Enum.ProxyHealthFilter.All" xml:space="preserve">
+    <value>All</value>
+  </data>
+  <data name="Enum.ProxyHealthFilter.Alive" xml:space="preserve">
+    <value>Alive</value>
+  </data>
+  <data name="Enum.ProxyHealthFilter.Dead" xml:space="preserve">
+    <value>Dead</value>
+  </data>
+  <data name="Enum.ProxyHealthFilter.Unchecked" xml:space="preserve">
+    <value>Unchecked</value>
+  </data>
+  <data name="Parser.delimited.Name" xml:space="preserve">
+    <value>Delimited text</value>
+  </data>
+  <data name="Parser.delimited.Description" xml:space="preserve">
+    <value>First non-empty line is the header. Rows are split on the delimiter that dominates it (, ; tab |).</value>
+  </data>
+  <data name="Parser.key-value.Name" xml:space="preserve">
+    <value>Key / value pairs</value>
+  </data>
+  <data name="Parser.key-value.Description" xml:space="preserve">
+    <value>One pair per line, separated by '=' or ':'. Lines starting with '#' are comments.</value>
+  </data>
+  <data name="Parse.Error.FieldCount" xml:space="preserve">
+    <value>Expected {0} field(s) but found {1}.</value>
+  </data>
+  <data name="Parse.Error.NoHeader" xml:space="preserve">
+    <value>Input contains no header row.</value>
+  </data>
+  <data name="Parse.Error.NoSeparator" xml:space="preserve">
+    <value>No '=' or ':' separator found.</value>
+  </data>
+  <data name="Parse.Error.EmptyKey" xml:space="preserve">
+    <value>Key is empty.</value>
+  </data>
+</root>

src/AvParser.UI/Localization/Strings.ru.resx

@@ -0,0 +1,490 @@
+<?xml version="1.0" encoding="utf-8"?>
+<root>
+  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
+    <xsd:import namespace="http://www.w3.org/XML/1998/namespace" />
+    <xsd:element name="root" msdata:IsDataSet="true">
+      <xsd:complexType>
+        <xsd:choice maxOccurs="unbounded">
+          <xsd:element name="metadata">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" />
+              </xsd:sequence>
+              <xsd:attribute name="name" use="required" type="xsd:string" />
+              <xsd:attribute name="type" type="xsd:string" />
+              <xsd:attribute name="mimetype" type="xsd:string" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="assembly">
+            <xsd:complexType>
+              <xsd:attribute name="alias" type="xsd:string" />
+              <xsd:attribute name="name" type="xsd:string" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="data">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+                <xsd:element name="comment" type="xsd:string" minOccurs="0" msdata:Ordinal="2" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" msdata:Ordinal="1" />
+              <xsd:attribute name="type" type="xsd:string" msdata:Ordinal="3" />
+              <xsd:attribute name="mimetype" type="xsd:string" msdata:Ordinal="4" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="resheader">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" />
+            </xsd:complexType>
+          </xsd:element>
+        </xsd:choice>
+      </xsd:complexType>
+    </xsd:element>
+  </xsd:schema>
+  <resheader name="resmimetype">
+    <value>text/microsoft-resx</value>
+  </resheader>
+  <resheader name="version">
+    <value>2.0</value>
+  </resheader>
+  <resheader name="reader">
+    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <resheader name="writer">
+    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <data name="Shell.ToggleNavigation" xml:space="preserve">
+    <value>Показать или скрыть навигацию</value>
+  </data>
+  <data name="Shell.Back" xml:space="preserve">
+    <value>Назад</value>
+  </data>
+  <data name="Shell.ToggleTheme" xml:space="preserve">
+    <value>Переключить светлую и тёмную тему</value>
+  </data>
+  <data name="Page.Dashboard" xml:space="preserve">
+    <value>Обзор</value>
+  </data>
+  <data name="Page.Parse" xml:space="preserve">
+    <value>Разбор</value>
+  </data>
+  <data name="Page.Proxies" xml:space="preserve">
+    <value>Прокси</value>
+  </data>
+  <data name="Page.Settings" xml:space="preserve">
+    <value>Настройки</value>
+  </data>
+  <data name="Page.About" xml:space="preserve">
+    <value>О программе</value>
+  </data>
+  <data name="Dashboard.Tagline" xml:space="preserve">
+    <value>Оболочка парсера с адаптивной раскладкой. Сузьте окно — навигация свернётся сначала в рельс из иконок, а затем в выезжающую панель.</value>
+  </data>
+  <data name="Dashboard.RegisteredParsers" xml:space="preserve">
+    <value>Доступные парсеры</value>
+  </data>
+  <data name="Dashboard.GetStarted" xml:space="preserve">
+    <value>С чего начать</value>
+  </data>
+  <data name="Dashboard.OpenParser" xml:space="preserve">
+    <value>Открыть парсер</value>
+  </data>
+  <data name="Dashboard.DataDirectory" xml:space="preserve">
+    <value>КАТАЛОГ ДАННЫХ</value>
+  </data>
+  <data name="Parse.Parser" xml:space="preserve">
+    <value>ПАРСЕР</value>
+  </data>
+  <data name="Parse.Actions" xml:space="preserve">
+    <value>ДЕЙСТВИЯ</value>
+  </data>
+  <data name="Parse.Run" xml:space="preserve">
+    <value>Разобрать</value>
+  </data>
+  <data name="Parse.Cancel" xml:space="preserve">
+    <value>Отменить</value>
+  </data>
+  <data name="Parse.Sample" xml:space="preserve">
+    <value>Пример</value>
+  </data>
+  <data name="Parse.SampleTip" xml:space="preserve">
+    <value>Подставить небольшой пример</value>
+  </data>
+  <data name="Parse.LargeSample" xml:space="preserve">
+    <value>50k строк</value>
+  </data>
+  <data name="Parse.LargeSampleTip" xml:space="preserve">
+    <value>Сгенерировать 50 000 строк, чтобы были видны прогресс и отмена</value>
+  </data>
+  <data name="Parse.ClearTip" xml:space="preserve">
+    <value>Очистить ввод и результаты</value>
+  </data>
+  <data name="Parse.Input" xml:space="preserve">
+    <value>ВХОД</value>
+  </data>
+  <data name="Parse.InputPlaceholder" xml:space="preserve">
+    <value>Вставьте текст или нажмите «Пример»</value>
+  </data>
+  <data name="Parse.Records" xml:space="preserve">
+    <value>ЗАПИСИ</value>
+  </data>
+  <data name="Parse.Errors" xml:space="preserve">
+    <value>ОШИБКИ</value>
+  </data>
+  <data name="Parse.Count.Records.One" xml:space="preserve">
+    <value>{0} запись</value>
+  </data>
+  <data name="Parse.Count.Records.Few" xml:space="preserve">
+    <value>{0} записи</value>
+  </data>
+  <data name="Parse.Count.Records.Many" xml:space="preserve">
+    <value>{0} записей</value>
+  </data>
+  <data name="Parse.Count.Errors.One" xml:space="preserve">
+    <value>{0} ошибка</value>
+  </data>
+  <data name="Parse.Count.Errors.Few" xml:space="preserve">
+    <value>{0} ошибки</value>
+  </data>
+  <data name="Parse.Count.Errors.Many" xml:space="preserve">
+    <value>{0} ошибок</value>
+  </data>
+  <data name="Parse.Status.Done" xml:space="preserve">
+    <value>Разобрано: {0} за {1} мс.</value>
+  </data>
+  <data name="Parse.Status.Cancelled" xml:space="preserve">
+    <value>Отменено: {0} за {1} мс.</value>
+  </data>
+  <data name="Parse.Status.WithErrors" xml:space="preserve">
+    <value>{0}, {1}.</value>
+  </data>
+  <data name="Parse.Status.Truncated" xml:space="preserve">
+    <value>Показаны только первые {0}.</value>
+  </data>
+  <data name="Parse.Status.Failed" xml:space="preserve">
+    <value>Разбор не удался: {0}</value>
+  </data>
+  <data name="Proxies.Pool" xml:space="preserve">
+    <value>ПУЛ</value>
+  </data>
+  <data name="Proxies.Refresh" xml:space="preserve">
+    <value>Обновить</value>
+  </data>
+  <data name="Proxies.RefreshTip" xml:space="preserve">
+    <value>Перечитать все источники</value>
+  </data>
+  <data name="Proxies.CheckAll" xml:space="preserve">
+    <value>Проверить все</value>
+  </data>
+  <data name="Proxies.CheckAllTip" xml:space="preserve">
+    <value>Проверить каждую прокси в пуле</value>
+  </data>
+  <data name="Proxies.Search" xml:space="preserve">
+    <value>ПОИСК</value>
+  </data>
+  <data name="Proxies.SearchPlaceholder" xml:space="preserve">
+    <value>адрес или страна</value>
+  </data>
+  <data name="Proxies.Protocol" xml:space="preserve">
+    <value>ПРОТОКОЛ</value>
+  </data>
+  <data name="Proxies.StatusColumn" xml:space="preserve">
+    <value>СОСТОЯНИЕ</value>
+  </data>
+  <data name="Proxies.Alive" xml:space="preserve">
+    <value>живых</value>
+  </data>
+  <data name="Proxies.Total" xml:space="preserve">
+    <value>всего</value>
+  </data>
+  <data name="Proxies.Matched" xml:space="preserve">
+    <value>найдено</value>
+  </data>
+  <data name="Proxies.ListHeader" xml:space="preserve">
+    <value>ПРОКСИ</value>
+  </data>
+  <data name="Proxies.CustomHeader" xml:space="preserve">
+    <value>СВОИ ПРОКСИ</value>
+  </data>
+  <data name="Proxies.Add" xml:space="preserve">
+    <value>Добавить</value>
+  </data>
+  <data name="Proxies.Remove" xml:space="preserve">
+    <value>Удалить</value>
+  </data>
+  <data name="Proxies.RemoveTip" xml:space="preserve">
+    <value>Удалить выбранную свою прокси</value>
+  </data>
+  <data name="Proxies.ClearTip" xml:space="preserve">
+    <value>Очистить свой список</value>
+  </data>
+  <data name="Proxies.CustomHint" xml:space="preserve">
+    <value>По одной в строке. scheme://host:port или host:port для обычного HTTP. Поддерживается user:pass@.</value>
+  </data>
+  <data name="Proxies.Health.Alive" xml:space="preserve">
+    <value>живая</value>
+  </data>
+  <data name="Proxies.Health.Dead" xml:space="preserve">
+    <value>мёртвая</value>
+  </data>
+  <data name="Proxies.Health.Unchecked" xml:space="preserve">
+    <value>не проверена</value>
+  </data>
+  <data name="Proxies.Source.Feed" xml:space="preserve">
+    <value>фид</value>
+  </data>
+  <data name="Proxies.Source.Custom" xml:space="preserve">
+    <value>своя</value>
+  </data>
+  <data name="Proxies.Count.Proxies.One" xml:space="preserve">
+    <value>{0} прокси</value>
+  </data>
+  <data name="Proxies.Count.Proxies.Few" xml:space="preserve">
+    <value>{0} прокси</value>
+  </data>
+  <data name="Proxies.Count.Proxies.Many" xml:space="preserve">
+    <value>{0} прокси</value>
+  </data>
+  <data name="Proxies.Status.PoolHolds" xml:space="preserve">
+    <value>В пуле {0}.</value>
+  </data>
+  <data name="Proxies.Status.Nothing" xml:space="preserve">
+    <value>Нечего добавлять.</value>
+  </data>
+  <data name="Proxies.Status.Added" xml:space="preserve">
+    <value>Добавлено {0} из {1}.</value>
+  </data>
+  <data name="Proxies.Status.Rejected" xml:space="preserve">
+    <value>Не удалось разобрать: {0}</value>
+  </data>
+  <data name="Proxies.Status.RejectedMore" xml:space="preserve">
+    <value>и ещё {0}</value>
+  </data>
+  <data name="Proxies.Status.Answered" xml:space="preserve">
+    <value>Ответили {0} из {1}.</value>
+  </data>
+  <data name="Proxies.Status.CheckCancelled" xml:space="preserve">
+    <value>Проверка отменена.</value>
+  </data>
+  <data name="Proxies.Status.Removed" xml:space="preserve">
+    <value>Удалено: {0}.</value>
+  </data>
+  <data name="Proxies.Status.Cleared" xml:space="preserve">
+    <value>Свой список очищен.</value>
+  </data>
+  <data name="Proxies.Status.Failed" xml:space="preserve">
+    <value>Ошибка: {0}</value>
+  </data>
+  <data name="Settings.Appearance" xml:space="preserve">
+    <value>Внешний вид</value>
+  </data>
+  <data name="Settings.Theme" xml:space="preserve">
+    <value>ТЕМА</value>
+  </data>
+  <data name="Settings.ThemeHint" xml:space="preserve">
+    <value>«Системная» следует настройке светлой или тёмной темы в ОС.</value>
+  </data>
+  <data name="Settings.Language" xml:space="preserve">
+    <value>ЯЗЫК</value>
+  </data>
+  <data name="Settings.LanguageHint" xml:space="preserve">
+    <value>Применяется сразу, перезапуск не нужен.</value>
+  </data>
+  <data name="Settings.Diagnostics" xml:space="preserve">
+    <value>Диагностика</value>
+  </data>
+  <data name="Settings.LogLevel" xml:space="preserve">
+    <value>МИНИМАЛЬНЫЙ УРОВЕНЬ ЛОГА</value>
+  </data>
+  <data name="Settings.LogLevelHint" xml:space="preserve">
+    <value>Применяется сразу, перезапуск не нужен.</value>
+  </data>
+  <data name="Settings.SettingsFile" xml:space="preserve">
+    <value>ФАЙЛ НАСТРОЕК</value>
+  </data>
+  <data name="Settings.LogDirectory" xml:space="preserve">
+    <value>КАТАЛОГ ЛОГОВ</value>
+  </data>
+  <data name="Settings.Proxies" xml:space="preserve">
+    <value>Прокси</value>
+  </data>
+  <data name="Settings.Rotation" xml:space="preserve">
+    <value>РОТАЦИЯ</value>
+  </data>
+  <data name="Settings.LivenessCheck" xml:space="preserve">
+    <value>ПРОВЕРКА ЖИВОСТИ</value>
+  </data>
+  <data name="Settings.UseFeed" xml:space="preserve">
+    <value>Использовать публичный фид proxifly</value>
+  </data>
+  <data name="Settings.ProbeUrl" xml:space="preserve">
+    <value>URL ДЛЯ ПРОВЕРКИ</value>
+  </data>
+  <data name="Settings.ProbeUrlHint" xml:space="preserve">
+    <value>По умолчанию обычный HTTP: требование TLS отбраковало бы все прокси без CONNECT, а не только нерабочие.</value>
+  </data>
+  <data name="Settings.ProbeTimeout" xml:space="preserve">
+    <value>ТАЙМАУТ ПРОВЕРКИ (СЕК)</value>
+  </data>
+  <data name="Settings.ProbeConcurrency" xml:space="preserve">
+    <value>ПРОВЕРОК ПАРАЛЛЕЛЬНО</value>
+  </data>
+  <data name="Settings.Rotation.Sticky" xml:space="preserve">
+    <value>Одна прокси на сессию, смена только при отказе. Не рвёт сессии сайтов.</value>
+  </data>
+  <data name="Settings.Rotation.RoundRobin" xml:space="preserve">
+    <value>Новая прокси на каждый запрос. Размазывает рейт-лимиты, но ломает сессионные cookie.</value>
+  </data>
+  <data name="Settings.Rotation.WeightedRandom" xml:space="preserve">
+    <value>Случайно, с весом по оценке из фида и по доле реально удачных запросов.</value>
+  </data>
+  <data name="Settings.HealthCheck.Pool" xml:space="preserve">
+    <value>Проверить весь пул заранее и параллельно. Один прогон — и дальше без задержек.</value>
+  </data>
+  <data name="Settings.HealthCheck.Lazy" xml:space="preserve">
+    <value>Проверять прокси в момент выдачи. Без прогона, но каждая выдача стоит одного запроса.</value>
+  </data>
+  <data name="Settings.Breakpoints" xml:space="preserve">
+    <value>Точки перелома раскладки</value>
+  </data>
+  <data name="Settings.BreakpointsHint" xml:space="preserve">
+    <value>Ширины окна, на которых меняется форма навигации. Измените размер окна, чтобы увидеть.</value>
+  </data>
+  <data name="Settings.Breakpoint.Compact" xml:space="preserve">
+    <value>КОМПАКТНАЯ</value>
+  </data>
+  <data name="Settings.Breakpoint.Medium" xml:space="preserve">
+    <value>СРЕДНЯЯ</value>
+  </data>
+  <data name="Settings.Breakpoint.Expanded" xml:space="preserve">
+    <value>ШИРОКАЯ</value>
+  </data>
+  <data name="Settings.Breakpoint.CompactHint" xml:space="preserve">
+    <value>меньше {0} px — выезжающая панель</value>
+  </data>
+  <data name="Settings.Breakpoint.MediumHint" xml:space="preserve">
+    <value>{0} – {1} px — рельс из иконок</value>
+  </data>
+  <data name="Settings.Breakpoint.ExpandedHint" xml:space="preserve">
+    <value>от {0} px — полная боковая панель</value>
+  </data>
+  <data name="About.BuiltWith" xml:space="preserve">
+    <value>Собрано на</value>
+  </data>
+  <data name="About.OnDisk" xml:space="preserve">
+    <value>На диске</value>
+  </data>
+  <data name="About.Data" xml:space="preserve">
+    <value>ДАННЫЕ</value>
+  </data>
+  <data name="About.Logs" xml:space="preserve">
+    <value>ЛОГИ</value>
+  </data>
+  <data name="About.Component.Dotnet" xml:space="preserve">
+    <value>.NET</value>
+  </data>
+  <data name="About.Component.Os" xml:space="preserve">
+    <value>Операционная система</value>
+  </data>
+  <data name="About.Component.Avalonia" xml:space="preserve">
+    <value>Avalonia</value>
+  </data>
+  <data name="About.Component.ReactiveUI" xml:space="preserve">
+    <value>ReactiveUI</value>
+  </data>
+  <data name="About.Component.Semi" xml:space="preserve">
+    <value>Semi.Avalonia</value>
+  </data>
+  <data name="About.Component.NotLoaded" xml:space="preserve">
+    <value>не загружено</value>
+  </data>
+  <data name="Enum.AppTheme.System" xml:space="preserve">
+    <value>Системная</value>
+  </data>
+  <data name="Enum.AppTheme.Light" xml:space="preserve">
+    <value>Светлая</value>
+  </data>
+  <data name="Enum.AppTheme.Dark" xml:space="preserve">
+    <value>Тёмная</value>
+  </data>
+  <data name="Enum.AppLanguage.System" xml:space="preserve">
+    <value>Системный</value>
+  </data>
+  <data name="Enum.AppLanguage.English" xml:space="preserve">
+    <value>English</value>
+  </data>
+  <data name="Enum.AppLanguage.Russian" xml:space="preserve">
+    <value>Русский</value>
+  </data>
+  <data name="Enum.ProxyRotation.Sticky" xml:space="preserve">
+    <value>Липкая</value>
+  </data>
+  <data name="Enum.ProxyRotation.RoundRobin" xml:space="preserve">
+    <value>По кругу</value>
+  </data>
+  <data name="Enum.ProxyRotation.WeightedRandom" xml:space="preserve">
+    <value>Случайная с весами</value>
+  </data>
+  <data name="Enum.ProxyHealthCheck.Pool" xml:space="preserve">
+    <value>Весь пул</value>
+  </data>
+  <data name="Enum.ProxyHealthCheck.Lazy" xml:space="preserve">
+    <value>При выдаче</value>
+  </data>
+  <data name="Enum.ProxyProtocolFilter.All" xml:space="preserve">
+    <value>Все</value>
+  </data>
+  <data name="Enum.ProxyProtocolFilter.Http" xml:space="preserve">
+    <value>HTTP</value>
+  </data>
+  <data name="Enum.ProxyProtocolFilter.Https" xml:space="preserve">
+    <value>HTTPS</value>
+  </data>
+  <data name="Enum.ProxyProtocolFilter.Socks4" xml:space="preserve">
+    <value>SOCKS4</value>
+  </data>
+  <data name="Enum.ProxyProtocolFilter.Socks5" xml:space="preserve">
+    <value>SOCKS5</value>
+  </data>
+  <data name="Enum.ProxyHealthFilter.All" xml:space="preserve">
+    <value>Все</value>
+  </data>
+  <data name="Enum.ProxyHealthFilter.Alive" xml:space="preserve">
+    <value>Живые</value>
+  </data>
+  <data name="Enum.ProxyHealthFilter.Dead" xml:space="preserve">
+    <value>Мёртвые</value>
+  </data>
+  <data name="Enum.ProxyHealthFilter.Unchecked" xml:space="preserve">
+    <value>Не проверены</value>
+  </data>
+  <data name="Parser.delimited.Name" xml:space="preserve">
+    <value>Текст с разделителями</value>
+  </data>
+  <data name="Parser.delimited.Description" xml:space="preserve">
+    <value>Первая непустая строка — заголовок. Строки режутся по разделителю, преобладающему в нём (, ; таб |).</value>
+  </data>
+  <data name="Parser.key-value.Name" xml:space="preserve">
+    <value>Пары ключ / значение</value>
+  </data>
+  <data name="Parser.key-value.Description" xml:space="preserve">
+    <value>По паре в строке, разделитель «=» или «:». Строки с «#» — комментарии.</value>
+  </data>
+  <data name="Parse.Error.FieldCount" xml:space="preserve">
+    <value>Ожидалось полей: {0}, найдено: {1}.</value>
+  </data>
+  <data name="Parse.Error.NoHeader" xml:space="preserve">
+    <value>Во входных данных нет строки заголовка.</value>
+  </data>
+  <data name="Parse.Error.NoSeparator" xml:space="preserve">
+    <value>Не найден разделитель «=» или «:».</value>
+  </data>
+  <data name="Parse.Error.EmptyKey" xml:space="preserve">
+    <value>Пустой ключ.</value>
+  </data>
+</root>

src/AvParser.UI/Services/ILocalizationService.cs

@@ -0,0 +1,16 @@
+using AvParser.Core.Settings;
+
+namespace AvParser.UI.Services;
+
+/// <summary>Applies and persists the UI language.</summary>
+public interface ILocalizationService
+{
+    /// <summary>The language currently in effect.</summary>
+    AppLanguage Current { get; }
+
+    /// <summary>Emits the language, starting with the present value.</summary>
+    IObservable<AppLanguage> Changes { get; }
+
+    /// <summary>Applies a language to the running application and persists the choice.</summary>
+    void Apply(AppLanguage language);
+}

src/AvParser.UI/Services/LocalizationService.cs

@@ -0,0 +1,67 @@
+using System.Globalization;
+using Avalonia;
+using AvParser.Core.Settings;
+using AvParser.UI.Localization;
+using ReactiveUI.Primitives.Signals;
+using Semi.Avalonia;
+
+namespace AvParser.UI.Services;
+
+/// <inheritdoc cref="ILocalizationService" />
+public sealed class LocalizationService : ILocalizationService, IDisposable
+{
+    private readonly ISettingsService _settings;
+    private readonly BehaviorSignal<AppLanguage> _current;
+
+    /// <summary>Restores the persisted language and applies it immediately.</summary>
+    public LocalizationService(ISettingsService settings)
+    {
+        _settings = settings ?? throw new ArgumentNullException(nameof(settings));
+        _current = new BehaviorSignal<AppLanguage>(settings.Current.Language);
+
+        ApplyToApplication(settings.Current.Language);
+    }
+
+    /// <inheritdoc />
+    public AppLanguage Current => _current.Value;
+
+    /// <inheritdoc />
+    public IObservable<AppLanguage> Changes => _current;
+
+    /// <inheritdoc />
+    public void Apply(AppLanguage language)
+    {
+        if (language == _current.Value)
+        {
+            return;
+        }
+
+        ApplyToApplication(language);
+        _current.OnNext(language);
+        _settings.Update(current => current with { Language = language });
+    }
+
+    /// <inheritdoc />
+    public void Dispose() => _current.Dispose();
+
+    private static void ApplyToApplication(AppLanguage language)
+    {
+        var culture = AppLanguages.ToCulture(language);
+
+        Localizer.Instance.SetLanguage(language);
+
+        // Number and date formatting has to move with the language, or a Russian UI would still
+        // print "50,000" with an English group separator.
+        CultureInfo.DefaultThreadCurrentCulture = culture;
+        CultureInfo.DefaultThreadCurrentUICulture = culture;
+        CultureInfo.CurrentCulture = culture;
+        CultureInfo.CurrentUICulture = culture;
+
+        // Semi ships its own strings for built-in controls; without this its dialogs and pickers
+        // stay English while everything around them changes.
+        if (Application.Current is { } app)
+        {
+            SemiTheme.OverrideLocaleResources(app, culture);
+        }
+    }
+}

src/AvParser.UI/ViewModels/AboutViewModel.cs

@@ -1,5 +1,7 @@
 using System.Reflection;
 using AvParser.Infrastructure.Storage;
+using AvParser.UI.Localization;
+using ReactiveUI;
 
 namespace AvParser.UI.ViewModels;
 
@@ -11,6 +13,8 @@ public sealed record ComponentInfo(string Name, string Detail);
 /// <summary>Version, runtime and stack information.</summary>
 public sealed class AboutViewModel : PageViewModel
 {
+    private readonly IReadOnlyList<(string Key, string Detail)> _components;
+
     /// <summary>Creates the page.</summary>
     public AboutViewModel(IAppPaths paths)
     {
@@ -33,18 +37,20 @@ public sealed class AboutViewModel : PageViewModel
         DataDirectory = paths.DataDirectory;
         LogDirectory = paths.LogDirectory;
 
-        Components =
+        _components =
         [
-            new ComponentInfo(".NET", Environment.Version.ToString()),
+            ("About.Component.Dotnet", Environment.Version.ToString()),
-            new ComponentInfo("Operating system", Environment.OSVersion.ToString()),
+            ("About.Component.Os", Environment.OSVersion.ToString()),
-            new ComponentInfo("Avalonia", VersionOf("Avalonia.Base")),
+            ("About.Component.Avalonia", VersionOf("Avalonia.Base")),
-            new ComponentInfo("ReactiveUI", VersionOf("ReactiveUI")),
+            ("About.Component.ReactiveUI", VersionOf("ReactiveUI")),
-            new ComponentInfo("Semi.Avalonia", VersionOf("Semi.Avalonia")),
+            ("About.Component.Semi", VersionOf("Semi.Avalonia")),
         ];
+
+        Components = Build(_components);
     }
 
     /// <inheritdoc />
-    public override string Title => "About";
+    public override string TitleKey => "Page.About";
 
     /// <inheritdoc />
     public override string IconKey => "IconInfo";
@@ -59,7 +65,21 @@ public sealed class AboutViewModel : PageViewModel
     public string LogDirectory { get; }
 
     /// <summary>The stack this build is running on.</summary>
-    public IReadOnlyList<ComponentInfo> Components { get; }
+    public IReadOnlyList<ComponentInfo> Components { get; private set; }
+
+    /// <inheritdoc />
+    protected override void OnLanguageChanged()
+    {
+        base.OnLanguageChanged();
+
+        // Component names are translated but their values are not, so rebuild the pairs rather
+        // than making ComponentInfo itself language-aware.
+        Components = Build(_components);
+        this.RaisePropertyChanged(nameof(Components));
+    }
+
+    private static IReadOnlyList<ComponentInfo> Build(IReadOnlyList<(string Key, string Detail)> components) =>
+        [.. components.Select(component => new ComponentInfo(Localizer.Instance[component.Key], component.Detail))];
 
     private static string VersionOf(string assemblyName)
     {

src/AvParser.UI/ViewModels/DashboardViewModel.cs

@@ -27,7 +27,7 @@ public sealed class DashboardViewModel : PageViewModel
 
         _services = services ?? throw new ArgumentNullException(nameof(services));
 
-        Parsers = catalog.Parsers;
+        Parsers = [.. catalog.Parsers.Select(parser => new ParserViewModel(parser))];
         DataDirectory = paths.DataDirectory;
 
         GoToParseCommand = ReactiveCommand.Create(() => Navigate<ParseViewModel>());
@@ -35,13 +35,13 @@ public sealed class DashboardViewModel : PageViewModel
     }
 
     /// <inheritdoc />
-    public override string Title => "Dashboard";
+    public override string TitleKey => "Page.Dashboard";
 
     /// <inheritdoc />
     public override string IconKey => "IconHome";
 
     /// <summary>Registered parsers, shown as cards.</summary>
-    public IReadOnlyList<ITextParser> Parsers { get; }
+    public IReadOnlyList<ParserViewModel> Parsers { get; }
 
     /// <summary>Where settings and logs are written.</summary>
     public string DataDirectory { get; }

src/AvParser.UI/ViewModels/ParseErrorViewModel.cs

@@ -0,0 +1,40 @@
+using AvParser.Core.Parsing;
+using AvParser.UI.Localization;
+using ReactiveUI;
+
+namespace AvParser.UI.ViewModels;
+
+/// <summary>One row of the parse error list, with its message translated.</summary>
+/// <remarks>
+/// Parsers are part of the domain and produce English text plus a code. This resolves
+/// <c>Parse.Error.{Code}</c> and falls back to the parser's own wording, so a parser that has not
+/// been translated yet still says something useful instead of showing a missing-key marker.
+/// </remarks>
+public sealed class ParseErrorViewModel(ParseError error) : ReactiveObject
+{
+    /// <summary>The underlying error.</summary>
+    public ParseError Error { get; } = error ?? throw new ArgumentNullException(nameof(error));
+
+    /// <summary>1-based position of the offending record.</summary>
+    public int LineNumber => Error.LineNumber;
+
+    /// <summary>Translated message.</summary>
+    public string Text
+    {
+        get
+        {
+            if (Error.Code is not { Length: > 0 } code)
+            {
+                return Error.Message;
+            }
+
+            var template = Localizer.Instance.GetOrDefault($"Parse.Error.{code}", Error.Message);
+            return Error.Arguments.Count == 0
+                ? template
+                : string.Format(Localizer.Instance.Culture, template, [.. Error.Arguments]);
+        }
+    }
+
+    /// <summary>Re-reads the translated message.</summary>
+    public void Refresh() => this.RaisePropertyChanged(nameof(Text));
+}

src/AvParser.UI/ViewModels/ParseViewModel.cs

@@ -4,6 +4,7 @@ using System.Globalization;
 using System.Text;
 using AvParser.Core.Parsing;
 using AvParser.Core.Settings;
+using AvParser.UI.Localization;
 using Microsoft.Extensions.Logging;
 using ReactiveUI;
 using ReactiveUI.Primitives;
@@ -42,7 +43,7 @@ public partial class ParseViewModel : PageViewModel
 
     /// <summary>Parser applied by <see cref="ParseCommand"/>.</summary>
     [Reactive]
-    public partial ITextParser SelectedParser { get; set; }
+    public partial ParserViewModel SelectedParser { get; set; }
 
     /// <summary>Completion of the running parse, 0.0 to 1.0.</summary>
     [Reactive]
@@ -73,7 +74,8 @@ public partial class ParseViewModel : PageViewModel
         _mainThread = mainThread ?? RxSchedulers.MainThreadScheduler;
 
         InputText = string.Empty;
-        SelectedParser = catalog.FindOrDefault(settings.Current.LastParserId);
+        Parsers = [.. catalog.Parsers.Select(parser => new ParserViewModel(parser))];
+        SelectedParser = Parsers.First(parser => parser.Id == catalog.FindOrDefault(settings.Current.LastParserId).Id);
 
         var canParse = this.WhenAnyValue(x => x.InputText)
             .Select(static text => !string.IsNullOrWhiteSpace(text))
@@ -118,19 +120,19 @@ public partial class ParseViewModel : PageViewModel
     }
 
     /// <inheritdoc />
-    public override string Title => "Parse";
+    public override string TitleKey => "Page.Parse";
 
     /// <inheritdoc />
     public override string IconKey => "IconDocument";
 
     /// <summary>Every registered parser, for the picker.</summary>
-    public IReadOnlyList<ITextParser> Parsers => _catalog.Parsers;
+    public IReadOnlyList<ParserViewModel> Parsers { get; }
 
     /// <summary>Successfully parsed records, capped at <see cref="MaxDisplayedRecords"/>.</summary>
     public ObservableCollection<ParsedRecord> Records { get; } = [];
 
     /// <summary>Per-line failures. A failure never aborts the parse.</summary>
-    public ObservableCollection<ParseError> Errors { get; } = [];
+    public ObservableCollection<ParseErrorViewModel> Errors { get; } = [];
 
     /// <summary>Whether a parse is currently running.</summary>
     public bool IsBusy => _isBusy.Value;
@@ -155,7 +157,7 @@ public partial class ParseViewModel : PageViewModel
         using var cancellation = CancellationTokenSource.CreateLinkedTokenSource(commandToken);
         _cancellation = cancellation;
 
-        var parser = SelectedParser;
+        var parser = SelectedParser.Parser;
         var input = InputText;
         var token = cancellation.Token;
 
@@ -228,29 +230,33 @@ public partial class ParseViewModel : PageViewModel
         );
     }
 
-    private static string BuildSummary(int succeeded, int failed, TimeSpan elapsed, bool truncated, bool cancelled)
+    /// <summary>
+    /// Builds the outcome line out of translated fragments.
+    /// </summary>
+    /// <remarks>
+    /// Assembled from plural-aware pieces rather than one format string per case: Russian needs
+    /// three forms for a counted noun, so "{0} records" with an English plural glued on cannot be
+    /// translated correctly.
+    /// </remarks>
+    internal static string BuildSummary(int succeeded, int failed, TimeSpan elapsed, bool truncated, bool cancelled)
     {
-        var text = new StringBuilder();
+        var loc = Localizer.Instance;
-        text.Append(cancelled ? "Cancelled after " : "Parsed ");
+        var records = loc.Plural("Parse.Count.Records", succeeded);
-        text.Append(succeeded.ToString("N0", CultureInfo.CurrentCulture));
+        var milliseconds = elapsed.TotalMilliseconds.ToString("N0", CultureInfo.CurrentCulture);
-        text.Append(succeeded == 1 ? " record" : " records");
+
+        var text = loc.Format(cancelled ? "Parse.Status.Cancelled" : "Parse.Status.Done", records, milliseconds);
 
         if (failed > 0)
         {
-            text.Append(", ").Append(failed.ToString("N0", CultureInfo.CurrentCulture));
+            text = loc.Format("Parse.Status.WithErrors", text.TrimEnd('.'), loc.Plural("Parse.Count.Errors", failed));
-            text.Append(failed == 1 ? " error" : " errors");
         }
 
-        text.Append(" in ").Append(elapsed.TotalMilliseconds.ToString("N0", CultureInfo.CurrentCulture)).Append(" ms");
-
         if (truncated)
         {
-            text.Append(" — showing the first ")
+            text += " " + loc.Format("Parse.Status.Truncated", loc.Plural("Parse.Count.Records", MaxDisplayedRecords));
-                .Append(MaxDisplayedRecords.ToString("N0", CultureInfo.CurrentCulture))
-                .Append(" only");
         }
 
-        return text.Append('.').ToString();
+        return text;
     }
 
     private void FlushBuffers(List<ParsedRecord> records, List<ParseError> errors)
@@ -275,11 +281,25 @@ public partial class ParseViewModel : PageViewModel
 
             foreach (var error in errorBatch)
             {
-                Errors.Add(error);
+                Errors.Add(new ParseErrorViewModel(error));
             }
         });
     }
 
+    /// <inheritdoc />
+    protected override void OnLanguageChanged()
+    {
+        base.OnLanguageChanged();
+
+        // The summary and the listed errors were both rendered in the previous language.
+        StatusMessage = null;
+
+        foreach (var error in Errors)
+        {
+            error.Refresh();
+        }
+    }
+
     private void ClearResults()
     {
         Records.Clear();
@@ -289,7 +309,7 @@ public partial class ParseViewModel : PageViewModel
     private void OnCommandFailed(Exception exception)
     {
         _logger.LogError(exception, "Parse failed");
-        OnUi(() => StatusMessage = $"Parse failed: {exception.Message}");
+        OnUi(() => StatusMessage = Localizer.Instance.Format("Parse.Status.Failed", exception.Message));
     }
 
     /// <summary>Marshals a mutation onto the UI thread; the parse loop runs on the thread pool.</summary>

src/AvParser.UI/ViewModels/ParserViewModel.cs

@@ -0,0 +1,43 @@
+using AvParser.Core.Parsing;
+using AvParser.UI.Localization;
+using ReactiveUI;
+
+namespace AvParser.UI.ViewModels;
+
+/// <summary>A parser paired with its translated name and description.</summary>
+/// <remarks>
+/// The domain deliberately knows nothing about languages, so <see cref="ITextParser"/> carries
+/// English text. This looks the id up as <c>Parser.{id}.Name</c> and falls back to what the parser
+/// itself says, which keeps the "add a parser = one registration line" promise intact: a new
+/// parser works untranslated instead of rendering a missing-key marker.
+/// </remarks>
+public sealed class ParserViewModel : ReactiveObject
+{
+    /// <summary>Wraps a parser.</summary>
+    public ParserViewModel(ITextParser parser)
+    {
+        Parser = parser ?? throw new ArgumentNullException(nameof(parser));
+        Localizer.Instance.LanguageChanged += OnLanguageChanged;
+    }
+
+    /// <summary>The parser itself.</summary>
+    public ITextParser Parser { get; }
+
+    /// <summary>Stable identifier.</summary>
+    public string Id => Parser.Id;
+
+    /// <summary>Translated name, or the parser's own when untranslated.</summary>
+    public string Name => Localizer.Instance.GetOrDefault($"Parser.{Id}.Name", Parser.DisplayName);
+
+    /// <summary>Translated description, or the parser's own when untranslated.</summary>
+    public string Description => Localizer.Instance.GetOrDefault($"Parser.{Id}.Description", Parser.Description);
+
+    /// <inheritdoc />
+    public override string ToString() => Name;
+
+    private void OnLanguageChanged(object? sender, EventArgs e)
+    {
+        this.RaisePropertyChanged(nameof(Name));
+        this.RaisePropertyChanged(nameof(Description));
+    }
+}

src/AvParser.UI/ViewModels/ProxiesViewModel.cs

@@ -2,6 +2,7 @@ using System.Collections.ObjectModel;
 using System.Globalization;
 using AvParser.Core.Proxies;
 using AvParser.Infrastructure.Proxies;
+using AvParser.UI.Localization;
 using Microsoft.Extensions.Logging;
 using ReactiveUI;
 using ReactiveUI.Primitives;
@@ -49,11 +50,11 @@ public partial class ProxiesViewModel : PageViewModel, IDisposable
 
     /// <summary>Protocol filter; <see cref="ProxyProtocolFilter.All"/> means no filtering.</summary>
     [Reactive]
-    public partial ProxyProtocolFilter ProtocolFilter { get; set; }
+    public partial LocalizedOption<ProxyProtocolFilter> ProtocolFilter { get; set; }
 
     /// <summary>Health filter.</summary>
     [Reactive]
-    public partial ProxyHealthFilter HealthFilter { get; set; }
+    public partial LocalizedOption<ProxyHealthFilter> HealthFilter { get; set; }
 
     /// <summary>Text box contents for adding custom proxies.</summary>
     [Reactive]
@@ -106,8 +107,8 @@ public partial class ProxiesViewModel : PageViewModel, IDisposable
 
         SearchText = string.Empty;
         NewProxies = string.Empty;
-        ProtocolFilter = ProxyProtocolFilter.All;
+        ProtocolFilter = ProtocolFilters[0];
-        HealthFilter = ProxyHealthFilter.All;
+        HealthFilter = HealthFilters[0];
 
         var idle = this.WhenAnyValue(x => x.IsSweeping).Select(static sweeping => !sweeping);
 
@@ -147,7 +148,7 @@ public partial class ProxiesViewModel : PageViewModel, IDisposable
     }
 
     /// <inheritdoc />
-    public override string Title => "Proxies";
+    public override string TitleKey => "Page.Proxies";
 
     /// <inheritdoc />
     public override string IconKey => "IconShield";
@@ -156,18 +157,18 @@ public partial class ProxiesViewModel : PageViewModel, IDisposable
     public ObservableCollection<ProxyRowViewModel> Proxies { get; } = [];
 
     /// <summary>Protocol filter options.</summary>
-    public IReadOnlyList<ProxyProtocolFilter> ProtocolFilters { get; } =
+    public IReadOnlyList<LocalizedOption<ProxyProtocolFilter>> ProtocolFilters { get; } =
-    [
+        LocalizedOption<ProxyProtocolFilter>.For(
-        ProxyProtocolFilter.All,
+            ProxyProtocolFilter.All,
-        ProxyProtocolFilter.Http,
+            ProxyProtocolFilter.Http,
-        ProxyProtocolFilter.Https,
+            ProxyProtocolFilter.Https,
-        ProxyProtocolFilter.Socks4,
+            ProxyProtocolFilter.Socks4,
-        ProxyProtocolFilter.Socks5,
+            ProxyProtocolFilter.Socks5
-    ];
+        );
 
     /// <summary>Health filter options.</summary>
-    public IReadOnlyList<ProxyHealthFilter> HealthFilters { get; } =
+    public IReadOnlyList<LocalizedOption<ProxyHealthFilter>> HealthFilters { get; } =
-    [ProxyHealthFilter.All, ProxyHealthFilter.Alive, ProxyHealthFilter.Dead, ProxyHealthFilter.Unchecked];
+        LocalizedOption<ProxyHealthFilter>.ForAll();
 
     /// <summary>Reloads every source into the pool.</summary>
     public ReactiveCommand<RxVoid, RxVoid> RefreshCommand { get; }
@@ -187,7 +188,12 @@ public partial class ProxiesViewModel : PageViewModel, IDisposable
     private async Task RefreshAsync(CancellationToken cancellationToken)
     {
         var count = await _pool.RefreshAsync(cancellationToken).ConfigureAwait(false);
-        OnUi(() => StatusMessage = $"Pool holds {Format(count)} prox{(count == 1 ? "y" : "ies")}.");
+        var message = Localizer.Instance.Format(
+            "Proxies.Status.PoolHolds",
+            Localizer.Instance.Plural("Proxies.Count.Proxies", count)
+        );
+
+        OnUi(() => StatusMessage = message);
     }
 
     private async Task SweepAsync(CancellationToken cancellationToken)
@@ -204,12 +210,13 @@ public partial class ProxiesViewModel : PageViewModel, IDisposable
             var progress = new Progress<ProxySweepProgress>(value => OnUi(() => SweepProgress = value.Fraction));
             var alive = await _pool.SweepAsync(progress, cancellationToken).ConfigureAwait(false);
             var total = _pool.Entries.Count;
+            var message = Localizer.Instance.Format("Proxies.Status.Answered", Format(alive), Format(total));
 
-            OnUi(() => StatusMessage = $"{Format(alive)} of {Format(total)} answered.");
+            OnUi(() => StatusMessage = message);
         }
         catch (OperationCanceledException)
         {
-            OnUi(() => StatusMessage = "Check cancelled.");
+            OnUi(() => StatusMessage = Localizer.Instance["Proxies.Status.CheckCancelled"]);
         }
         finally
         {
@@ -225,24 +232,28 @@ public partial class ProxiesViewModel : PageViewModel, IDisposable
     {
         var (parsed, rejected) = CustomProxySource.ParseList(NewProxies);
 
+        var loc = Localizer.Instance;
+
         if (parsed.Count == 0 && rejected.Count == 0)
         {
-            OnUi(() => StatusMessage = "Nothing to add.");
+            OnUi(() => StatusMessage = loc["Proxies.Status.Nothing"]);
             return;
         }
 
         var added = await _customSource.AddAsync(parsed, cancellationToken).ConfigureAwait(false);
         await _pool.RefreshAsync(cancellationToken).ConfigureAwait(false);
 
-        var message = $"Added {Format(added)} of {Format(parsed.Count)}.";
+        var message = loc.Format("Proxies.Status.Added", Format(added), Format(parsed.Count));
         if (rejected.Count > 0)
         {
             // Naming the first few beats "3 lines were invalid" when a paste is hundreds long.
-            message += $" Could not parse: {string.Join(", ", rejected.Take(3))}";
+            var sample = string.Join(", ", rejected.Take(3));
             if (rejected.Count > 3)
             {
-                message += $" and {Format(rejected.Count - 3)} more";
+                sample += " " + loc.Format("Proxies.Status.RejectedMore", Format(rejected.Count - 3));
             }
+
+            message += " " + loc.Format("Proxies.Status.Rejected", sample);
         }
 
         OnUi(() =>
@@ -265,7 +276,7 @@ public partial class ProxiesViewModel : PageViewModel, IDisposable
         await _customSource.RemoveAsync(row.Entry.Endpoint, cancellationToken).ConfigureAwait(false);
         await _pool.RefreshAsync(cancellationToken).ConfigureAwait(false);
 
-        OnUi(() => StatusMessage = $"Removed {row.Address}.");
+        OnUi(() => StatusMessage = Localizer.Instance.Format("Proxies.Status.Removed", row.Address));
     }
 
     private async Task ClearCustomAsync(CancellationToken cancellationToken)
@@ -273,7 +284,19 @@ public partial class ProxiesViewModel : PageViewModel, IDisposable
         await _customSource.ClearAsync(cancellationToken).ConfigureAwait(false);
         await _pool.RefreshAsync(cancellationToken).ConfigureAwait(false);
 
-        OnUi(() => StatusMessage = "Custom list cleared.");
+        OnUi(() => StatusMessage = Localizer.Instance["Proxies.Status.Cleared"]);
+    }
+
+    /// <inheritdoc />
+    protected override void OnLanguageChanged()
+    {
+        base.OnLanguageChanged();
+
+        // Health and source captions live on the rows, so they need the nudge individually.
+        foreach (var row in _rows.Values)
+        {
+            row.Refresh();
+        }
     }
 
     /// <inheritdoc />
@@ -333,14 +356,14 @@ public partial class ProxiesViewModel : PageViewModel, IDisposable
     private bool PassesFilters(ProxyRowViewModel row)
     {
         if (
-            ProtocolFilter != ProxyProtocolFilter.All
+            ProtocolFilter.Value != ProxyProtocolFilter.All
-            && !ProtocolFilter.HasFlag(ProxyOptions.ToFlag(row.Entry.Endpoint.Protocol))
+            && !ProtocolFilter.Value.HasFlag(ProxyOptions.ToFlag(row.Entry.Endpoint.Protocol))
         )
         {
             return false;
         }
 
-        var healthOk = HealthFilter switch
+        var healthOk = HealthFilter.Value switch
         {
             ProxyHealthFilter.Alive => row.Entry.Health == ProxyHealthState.Alive,
             ProxyHealthFilter.Dead => row.Entry.Health == ProxyHealthState.Dead,
@@ -354,7 +377,7 @@ public partial class ProxiesViewModel : PageViewModel, IDisposable
     private void OnCommandFailed(Exception exception)
     {
         _logger.LogError(exception, "Proxy action failed");
-        OnUi(() => StatusMessage = $"Failed: {exception.Message}");
+        OnUi(() => StatusMessage = Localizer.Instance.Format("Proxies.Status.Failed", exception.Message));
     }
 
     private static string Format(int value) => value.ToString("N0", CultureInfo.CurrentCulture);

src/AvParser.UI/ViewModels/ProxyRowViewModel.cs

@@ -1,5 +1,6 @@
 using System.Globalization;
 using AvParser.Core.Proxies;
+using AvParser.UI.Localization;
 using ReactiveUI;
 
 namespace AvParser.UI.ViewModels;
@@ -35,16 +36,18 @@ public sealed class ProxyRowViewModel(ProxyEntry entry) : ReactiveObject
     public bool IsCustom => Entry.Source == ProxySourceKind.Custom;
 
     /// <summary>Source label.</summary>
-    public string Source => IsCustom ? "custom" : "feed";
+    public string Source => Localizer.Instance[IsCustom ? "Proxies.Source.Custom" : "Proxies.Source.Feed"];
 
     /// <summary>Last known health, as a word.</summary>
     public string HealthText =>
-        Entry.Health switch
+        Localizer.Instance[
-        {
+            Entry.Health switch
-            ProxyHealthState.Alive => "alive",
+            {
-            ProxyHealthState.Dead => "dead",
+                ProxyHealthState.Alive => "Proxies.Health.Alive",
-            _ => "unchecked",
+                ProxyHealthState.Dead => "Proxies.Health.Dead",
-        };
+                _ => "Proxies.Health.Unchecked",
+            }
+        ];
 
     /// <summary>Whether the last check succeeded. Drives the row's accent.</summary>
     public bool IsAlive => Entry.Health == ProxyHealthState.Alive;
@@ -68,9 +71,10 @@ public sealed class ProxyRowViewModel(ProxyEntry entry) : ReactiveObject
     /// <summary>Whether the entry is sidelined right now.</summary>
     public bool IsQuarantined => Entry.QuarantinedUntilUtc is { } until && until > DateTimeOffset.UtcNow;
 
-    /// <summary>Re-reads everything that the pool can change behind our back.</summary>
+    /// <summary>Re-reads everything that the pool — or the language — can change behind our back.</summary>
     public void Refresh()
     {
+        this.RaisePropertyChanged(nameof(Source));
         this.RaisePropertyChanged(nameof(HealthText));
         this.RaisePropertyChanged(nameof(IsAlive));
         this.RaisePropertyChanged(nameof(IsDead));

src/AvParser.UI/ViewModels/SettingsViewModel.cs

@@ -2,6 +2,7 @@ using AvParser.Core.Proxies;
 using AvParser.Core.Settings;
 using AvParser.Infrastructure.Logging;
 using AvParser.Infrastructure.Storage;
+using AvParser.UI.Localization;
 using AvParser.UI.Responsive;
 using AvParser.UI.Services;
 using ReactiveUI;
@@ -19,10 +20,15 @@ public partial class SettingsViewModel : PageViewModel
     private readonly IThemeService _theme;
     private readonly LoggingLevelSwitch _levelSwitch;
     private readonly IProxyPool _proxyPool;
+    private readonly ILocalizationService _localization;
 
     /// <summary>Selected theme. Applied immediately, not on an OK button.</summary>
     [Reactive]
-    public partial AppTheme SelectedTheme { get; set; }
+    public partial LocalizedOption<AppTheme> SelectedTheme { get; set; }
+
+    /// <summary>Selected UI language. Applied immediately.</summary>
+    [Reactive]
+    public partial LocalizedOption<AppLanguage> SelectedLanguage { get; set; }
 
     /// <summary>Selected Serilog level name. Takes effect immediately.</summary>
     [Reactive]
@@ -30,11 +36,11 @@ public partial class SettingsViewModel : PageViewModel
 
     /// <summary>How the pool picks the next proxy.</summary>
     [Reactive]
-    public partial ProxyRotation SelectedRotation { get; set; }
+    public partial LocalizedOption<ProxyRotation> SelectedRotation { get; set; }
 
     /// <summary>When proxy liveness is verified.</summary>
     [Reactive]
-    public partial ProxyHealthCheck SelectedHealthCheck { get; set; }
+    public partial LocalizedOption<ProxyHealthCheck> SelectedHealthCheck { get; set; }
 
     /// <summary>Whether the remote proxy feed is consulted.</summary>
     [Reactive]
@@ -59,6 +65,7 @@ public partial class SettingsViewModel : PageViewModel
         IAppPaths paths,
         LoggingLevelSwitch levelSwitch,
         IProxyPool proxyPool,
+        ILocalizationService localization,
         ISequencer? mainThread = null
     )
     {
@@ -66,6 +73,7 @@ public partial class SettingsViewModel : PageViewModel
         _theme = theme ?? throw new ArgumentNullException(nameof(theme));
         _levelSwitch = levelSwitch ?? throw new ArgumentNullException(nameof(levelSwitch));
         _proxyPool = proxyPool ?? throw new ArgumentNullException(nameof(proxyPool));
+        _localization = localization ?? throw new ArgumentNullException(nameof(localization));
         ArgumentNullException.ThrowIfNull(paths);
 
         var scheduler = mainThread ?? RxSchedulers.MainThreadScheduler;
@@ -73,26 +81,31 @@ public partial class SettingsViewModel : PageViewModel
         SettingsFile = paths.SettingsFile;
         LogDirectory = paths.LogDirectory;
 
-        SelectedTheme = theme.Current;
+        SelectedTheme = Option(Themes, theme.Current);
+        SelectedLanguage = Option(Languages, localization.Current);
         SelectedLogLevel = settings.Current.MinimumLogLevel;
 
         var current = settings.Current;
-        SelectedRotation = current.ProxyRotation;
+        SelectedRotation = Option(Rotations, current.ProxyRotation);
-        SelectedHealthCheck = current.ProxyHealthCheck;
+        SelectedHealthCheck = Option(HealthChecks, current.ProxyHealthCheck);
         UseProxyFeed = current.ProxyUseFeed;
         ProxyProbeUrl = current.ProxyProbeUrl;
         ProxyProbeTimeoutSeconds = current.ProxyProbeTimeoutSeconds;
         ProxyProbeConcurrency = current.ProxyProbeConcurrency;
 
-        this.WhenAnyValue(x => x.SelectedTheme).ObserveOn(scheduler).Subscribe(_theme.Apply);
+        this.WhenAnyValue(x => x.SelectedTheme).ObserveOn(scheduler).Subscribe(option => _theme.Apply(option.Value));
+
+        this.WhenAnyValue(x => x.SelectedLanguage)
+            .ObserveOn(scheduler)
+            .Subscribe(option => _localization.Apply(option.Value));
 
         this.WhenAnyValue(x => x.SelectedLogLevel)
             .Where(static level => !string.IsNullOrEmpty(level))
             .DistinctUntilChanged()
             .Subscribe(ApplyLogLevel);
 
-        // Keep the radio group honest when the theme is flipped from the title-bar button.
+        // Keep the picker honest when the theme is flipped from the title-bar button.
-        theme.Changes.ObserveOn(scheduler).Subscribe(value => SelectedTheme = value);
+        theme.Changes.ObserveOn(scheduler).Subscribe(value => SelectedTheme = Option(Themes, value));
 
         // Every proxy knob funnels through one handler: they all end up rebuilding the same
         // ProxyOptions, and applying them one at a time would reconfigure the pool six times.
@@ -117,39 +130,42 @@ public partial class SettingsViewModel : PageViewModel
     }
 
     /// <inheritdoc />
-    public override string Title => "Settings";
+    public override string TitleKey => "Page.Settings";
 
     /// <inheritdoc />
     public override string IconKey => "IconSettings";
 
-    /// <summary>Theme options offered by the radio group.</summary>
+    /// <summary>Theme options offered by the picker.</summary>
-    public IReadOnlyList<AppTheme> Themes { get; } = [AppTheme.System, AppTheme.Light, AppTheme.Dark];
+    public IReadOnlyList<LocalizedOption<AppTheme>> Themes { get; } = LocalizedOption<AppTheme>.ForAll();
+
+    /// <summary>Language options offered by the picker.</summary>
+    public IReadOnlyList<LocalizedOption<AppLanguage>> Languages { get; } = LocalizedOption<AppLanguage>.ForAll();
 
     /// <summary>Serilog level names, most to least verbose.</summary>
     public IReadOnlyList<string> LogLevels => AppLogging.AvailableLevels;
 
     /// <summary>Rotation strategies offered by the picker.</summary>
-    public IReadOnlyList<ProxyRotation> Rotations { get; } =
+    public IReadOnlyList<LocalizedOption<ProxyRotation>> Rotations { get; } = LocalizedOption<ProxyRotation>.ForAll();
-    [ProxyRotation.Sticky, ProxyRotation.RoundRobin, ProxyRotation.WeightedRandom];
 
     /// <summary>Liveness policies offered by the picker.</summary>
-    public IReadOnlyList<ProxyHealthCheck> HealthChecks { get; } = [ProxyHealthCheck.Pool, ProxyHealthCheck.Lazy];
+    public IReadOnlyList<LocalizedOption<ProxyHealthCheck>> HealthChecks { get; } =
+        LocalizedOption<ProxyHealthCheck>.ForAll();
 
     /// <summary>Explains the selected rotation in one line.</summary>
-    public string RotationDescription =>
+    public string RotationDescription => Localizer.Instance[$"Settings.Rotation.{SelectedRotation.Value}"];
-        SelectedRotation switch
-        {
-            ProxyRotation.Sticky => "One proxy per session, replaced only when it fails. Keeps site sessions intact.",
-            ProxyRotation.RoundRobin =>
-                "A different proxy on every request. Spreads rate limits, but breaks session cookies.",
-            _ => "Random, weighted by feed score and how often the proxy has actually worked here.",
-        };
 
     /// <summary>Explains the selected health-check policy in one line.</summary>
-    public string HealthCheckDescription =>
+    public string HealthCheckDescription => Localizer.Instance[$"Settings.HealthCheck.{SelectedHealthCheck.Value}"];
-        SelectedHealthCheck == ProxyHealthCheck.Pool
+
-            ? "Probe the whole pool up front, in parallel. One sweep, then no per-request delay."
+    /// <summary>Describes the compact breakpoint band.</summary>
-            : "Probe each proxy as it is handed out. No sweep, but every acquisition pays a round trip.";
+    public string CompactHint => Localizer.Instance.Format("Settings.Breakpoint.CompactHint", MediumBreakpoint);
+
+    /// <summary>Describes the medium breakpoint band.</summary>
+    public string MediumHint =>
+        Localizer.Instance.Format("Settings.Breakpoint.MediumHint", MediumBreakpoint, ExpandedBreakpoint);
+
+    /// <summary>Describes the expanded breakpoint band.</summary>
+    public string ExpandedHint => Localizer.Instance.Format("Settings.Breakpoint.ExpandedHint", ExpandedBreakpoint);
 
     /// <summary>Full path of the settings file.</summary>
     public string SettingsFile { get; }
@@ -163,6 +179,29 @@ public partial class SettingsViewModel : PageViewModel
     /// <summary>Width in pixels at which the shell switches to the full sidebar.</summary>
     public double ExpandedBreakpoint => ResponsiveLayout.ExpandedMinWidth;
 
+    /// <inheritdoc />
+    protected override void OnLanguageChanged()
+    {
+        base.OnLanguageChanged();
+
+        foreach (
+            var name in new[]
+            {
+                nameof(RotationDescription),
+                nameof(HealthCheckDescription),
+                nameof(CompactHint),
+                nameof(MediumHint),
+                nameof(ExpandedHint),
+            }
+        )
+        {
+            this.RaisePropertyChanged(name);
+        }
+    }
+
+    private static LocalizedOption<TValue> Option<TValue>(IReadOnlyList<LocalizedOption<TValue>> options, TValue value)
+        where TValue : struct, Enum => options.First(option => option.Value.Equals(value));
+
     private void ApplyLogLevel(string level)
     {
         _levelSwitch.MinimumLevel = AppLogging.ParseLevel(level);
@@ -177,8 +216,8 @@ public partial class SettingsViewModel : PageViewModel
         {
             applied = current with
             {
-                ProxyRotation = SelectedRotation,
+                ProxyRotation = SelectedRotation.Value,
-                ProxyHealthCheck = SelectedHealthCheck,
+                ProxyHealthCheck = SelectedHealthCheck.Value,
                 ProxyUseFeed = UseProxyFeed,
                 ProxyProbeUrl = ProxyProbeUrl,
                 ProxyProbeTimeoutSeconds = ProxyProbeTimeoutSeconds,

src/AvParser.UI/ViewModels/ShellViewModel.cs

@@ -22,7 +22,6 @@ public partial class ShellViewModel : ViewModelBase
     private readonly IThemeService _theme;
     private readonly ObservableAsPropertyHelper<SplitViewDisplayMode> _paneDisplayMode;
     private readonly ObservableAsPropertyHelper<PageViewModel> _currentPage;
-    private readonly ObservableAsPropertyHelper<string> _title;
     private readonly ObservableAsPropertyHelper<bool> _canGoBack;
     private readonly ObservableAsPropertyHelper<string> _themeIconKey;
 
@@ -58,10 +57,6 @@ public partial class ShellViewModel : ViewModelBase
 
         _currentPage = navigation.CurrentChanges.ToProperty(this, nameof(CurrentPage), navigation.Current, scheduler);
 
-        _title = navigation
-            .CurrentChanges.Select(static page => page.Title)
-            .ToProperty(this, nameof(Title), navigation.Current.Title, scheduler);
-
         _canGoBack = navigation.CanGoBack.ToProperty(this, nameof(CanGoBack), false, scheduler);
 
         _paneDisplayMode = this.WhenAnyValue(x => x.Breakpoint)
@@ -85,6 +80,12 @@ public partial class ShellViewModel : ViewModelBase
             .Select(static breakpoint => breakpoint == Breakpoint.Expanded)
             .Subscribe(open => IsPaneOpen = open);
 
+        // The title tracks the page, and the page tracks the language.
+        this.WhenAnyValue(x => x.CurrentPage)
+            .Select(static page => page.WhenAnyValue(inner => inner.Title))
+            .Switch()
+            .Subscribe(_ => this.RaisePropertyChanged(nameof(Title)));
+
         // Rail selection drives navigation...
         this.WhenAnyValue(x => x.SelectedPage).Subscribe(_navigation.NavigateTo);
 
@@ -113,7 +114,12 @@ public partial class ShellViewModel : ViewModelBase
     public PageViewModel CurrentPage => _currentPage.Value;
 
     /// <summary>Title of the current page.</summary>
-    public string Title => _title.Value;
+    /// <remarks>
+    /// Read straight off the page rather than snapshotted into a derived property: the page
+    /// re-raises its own title when the language changes, and a snapshot would keep showing the
+    /// caption from the previous language until the user navigated somewhere else.
+    /// </remarks>
+    public string Title => CurrentPage.Title;
 
     /// <summary>Whether the back button is enabled.</summary>
     public bool CanGoBack => _canGoBack.Value;

src/AvParser.UI/ViewModels/ViewModelBase.cs

@@ -1,3 +1,4 @@
+using AvParser.UI.Localization;
 using ReactiveUI;
 
 namespace AvParser.UI.ViewModels;
@@ -17,11 +18,28 @@ public abstract class ViewModelBase : ReactiveObject, IActivatableViewModel
 /// <summary>A view model that appears as a top-level destination in the navigation rail.</summary>
 public abstract class PageViewModel : ViewModelBase
 {
-    /// <summary>Label shown in the sidebar and the title bar.</summary>
+    /// <summary>Creates the page and keeps its title in step with the language.</summary>
-    public abstract string Title { get; }
+    protected PageViewModel() => Localizer.Instance.LanguageChanged += OnLanguageChanged;
+
+    /// <summary>Resource key of the label shown in the sidebar and the title bar.</summary>
+    public abstract string TitleKey { get; }
+
+    /// <summary>Translated label.</summary>
+    public string Title => Localizer.Instance[TitleKey];
 
     /// <summary>
     /// Key of a <c>StreamGeometry</c> in <c>Styles/Icons.axaml</c> used as the rail icon.
     /// </summary>
     public abstract string IconKey { get; }
+
+    /// <summary>
+    /// Re-reads anything derived from the current language.
+    /// </summary>
+    /// <remarks>
+    /// Overriders must call the base: the rail and the title bar bind to <see cref="Title"/>, and
+    /// without the notification they would keep the caption from the previous language.
+    /// </remarks>
+    protected virtual void OnLanguageChanged() => this.RaisePropertyChanged(nameof(Title));
+
+    private void OnLanguageChanged(object? sender, EventArgs e) => OnLanguageChanged();
 }

src/AvParser.UI/Views/AboutView.axaml

@@ -1,6 +1,7 @@
 <UserControl
   xmlns="https://github.com/avaloniaui"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+  xmlns:l="clr-namespace:AvParser.UI.Localization"
   xmlns:vm="clr-namespace:AvParser.UI.ViewModels"
   x:Class="AvParser.UI.Views.AboutView"
   x:DataType="vm:AboutViewModel"
@@ -18,7 +19,7 @@
 
       <Border Classes="card">
         <StackPanel Spacing="12">
-          <TextBlock Classes="subtitle" Text="Built with" />
+          <TextBlock Classes="subtitle" Text="{l:Loc About.BuiltWith}" />
           <ItemsControl ItemsSource="{Binding Components}">
             <ItemsControl.ItemTemplate>
               <DataTemplate x:DataType="vm:ComponentInfo">
@@ -34,13 +35,13 @@
 
       <Border Classes="card">
         <StackPanel Spacing="12">
-          <TextBlock Classes="subtitle" Text="On disk" />
+          <TextBlock Classes="subtitle" Text="{l:Loc About.OnDisk}" />
           <StackPanel Spacing="6">
-            <TextBlock Classes="caption" Text="DATA" />
+            <TextBlock Classes="caption" Text="{l:Loc About.Data}" />
             <SelectableTextBlock Classes="mono" Text="{Binding DataDirectory}" TextWrapping="Wrap" />
           </StackPanel>
           <StackPanel Spacing="6">
-            <TextBlock Classes="caption" Text="LOGS" />
+            <TextBlock Classes="caption" Text="{l:Loc About.Logs}" />
             <SelectableTextBlock Classes="mono" Text="{Binding LogDirectory}" TextWrapping="Wrap" />
           </StackPanel>
         </StackPanel>

src/AvParser.UI/Views/DashboardView.axaml

@@ -1,8 +1,8 @@
 <UserControl
   xmlns="https://github.com/avaloniaui"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+  xmlns:l="clr-namespace:AvParser.UI.Localization"
   xmlns:vm="clr-namespace:AvParser.UI.ViewModels"
-  xmlns:parsing="clr-namespace:AvParser.Core.Parsing;assembly=AvParser.Core"
   x:Class="AvParser.UI.Views.DashboardView"
   x:DataType="vm:DashboardViewModel"
 >
@@ -10,15 +10,11 @@
     <StackPanel Spacing="24" MaxWidth="1040" HorizontalAlignment="Left">
       <StackPanel Spacing="6">
         <TextBlock Classes="display" Text="AvParser" />
-        <TextBlock
+        <TextBlock Classes="muted" MaxWidth="640" Text="{l:Loc Dashboard.Tagline}" />
-          Classes="muted"
-          MaxWidth="640"
-          Text="A parser shell with an adaptive layout. Drag the window narrower to watch the navigation collapse to an icon rail and then to an overlay drawer."
-        />
       </StackPanel>
 
       <StackPanel Spacing="12">
-        <TextBlock Classes="subtitle" Text="Registered parsers" />
+        <TextBlock Classes="subtitle" Text="{l:Loc Dashboard.RegisteredParsers}" />
         <ItemsControl ItemsSource="{Binding Parsers}">
           <ItemsControl.ItemsPanel>
             <ItemsPanelTemplate>
@@ -26,10 +22,10 @@
             </ItemsPanelTemplate>
           </ItemsControl.ItemsPanel>
           <ItemsControl.ItemTemplate>
-            <DataTemplate x:DataType="parsing:ITextParser">
+            <DataTemplate x:DataType="vm:ParserViewModel">
               <Border Classes="card interactive" Width="320" Margin="0,0,12,12">
                 <StackPanel Spacing="8">
-                  <TextBlock Classes="subtitle" Text="{Binding DisplayName}" />
+                  <TextBlock Classes="subtitle" Text="{Binding Name}" />
                   <Border Classes="chip accent" HorizontalAlignment="Left">
                     <TextBlock Classes="mono caption" Text="{Binding Id}" />
                   </Border>
@@ -42,18 +38,18 @@
       </StackPanel>
 
       <StackPanel Spacing="12">
-        <TextBlock Classes="subtitle" Text="Get started" />
+        <TextBlock Classes="subtitle" Text="{l:Loc Dashboard.GetStarted}" />
         <StackPanel Orientation="Horizontal" Spacing="12">
           <Button Classes="primary" Command="{Binding GoToParseCommand}">
             <StackPanel Orientation="Horizontal" Spacing="8">
               <PathIcon Classes="glyph" Data="{DynamicResource IconPlay}" />
-              <TextBlock Text="Open the parser" />
+              <TextBlock Text="{l:Loc Dashboard.OpenParser}" />
             </StackPanel>
           </Button>
           <Button Command="{Binding GoToSettingsCommand}">
             <StackPanel Orientation="Horizontal" Spacing="8">
               <PathIcon Classes="glyph" Data="{DynamicResource IconSettings}" />
-              <TextBlock Text="Settings" />
+              <TextBlock Text="{l:Loc Page.Settings}" />
             </StackPanel>
           </Button>
         </StackPanel>
@@ -61,7 +57,7 @@
 
       <Border Classes="card">
         <StackPanel Spacing="6">
-          <TextBlock Classes="caption" Text="DATA DIRECTORY" />
+          <TextBlock Classes="caption" Text="{l:Loc Dashboard.DataDirectory}" />
           <SelectableTextBlock Classes="mono" Text="{Binding DataDirectory}" TextWrapping="Wrap" />
         </StackPanel>
       </Border>

src/AvParser.UI/Views/ParseView.axaml

@@ -1,6 +1,7 @@
 <UserControl
   xmlns="https://github.com/avaloniaui"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+  xmlns:l="clr-namespace:AvParser.UI.Localization"
   xmlns:vm="clr-namespace:AvParser.UI.ViewModels"
   xmlns:conv="clr-namespace:AvParser.UI.Converters"
   xmlns:parsing="clr-namespace:AvParser.Core.Parsing;assembly=AvParser.Core"
@@ -13,7 +14,7 @@
       <StackPanel Spacing="12">
         <WrapPanel Orientation="Horizontal">
           <StackPanel Spacing="4" Margin="0,0,16,8" MinWidth="240">
-            <TextBlock Classes="caption" Text="PARSER" />
+            <TextBlock Classes="caption" Text="{l:Loc Parse.Parser}" />
             <ComboBox
               ItemsSource="{Binding Parsers}"
               SelectedItem="{Binding SelectedParser}"
@@ -21,42 +22,39 @@
               HorizontalAlignment="Stretch"
             >
               <ComboBox.ItemTemplate>
-                <DataTemplate x:DataType="parsing:ITextParser">
+                <DataTemplate x:DataType="vm:ParserViewModel">
-                  <TextBlock Text="{Binding DisplayName}" />
+                  <TextBlock Text="{Binding Name}" />
                 </DataTemplate>
               </ComboBox.ItemTemplate>
             </ComboBox>
           </StackPanel>
 
           <StackPanel Spacing="4" Margin="0,0,0,8">
-            <TextBlock Classes="caption" Text="ACTIONS" />
+            <TextBlock Classes="caption" Text="{l:Loc Parse.Actions}" />
             <StackPanel Orientation="Horizontal" Spacing="8">
               <Button Classes="primary" Command="{Binding ParseCommand}">
                 <StackPanel Orientation="Horizontal" Spacing="8">
                   <PathIcon Classes="glyph" Data="{DynamicResource IconPlay}" />
-                  <TextBlock Text="Parse" />
+                  <TextBlock Text="{l:Loc Parse.Run}" />
                 </StackPanel>
               </Button>
 
               <Button Classes="destructive" Command="{Binding CancelCommand}">
                 <StackPanel Orientation="Horizontal" Spacing="8">
                   <PathIcon Classes="glyph" Data="{DynamicResource IconStop}" />
-                  <TextBlock Text="Cancel" />
+                  <TextBlock Text="{l:Loc Parse.Cancel}" />
                 </StackPanel>
               </Button>
 
-              <Button Command="{Binding LoadSampleCommand}" ToolTip.Tip="Fill the input with a small example">
+              <Button Command="{Binding LoadSampleCommand}" ToolTip.Tip="{l:Loc Parse.SampleTip}">
-                <TextBlock Text="Sample" />
+                <TextBlock Text="{l:Loc Parse.Sample}" />
               </Button>
 
-              <Button
+              <Button Command="{Binding GenerateLargeSampleCommand}" ToolTip.Tip="{l:Loc Parse.LargeSampleTip}">
-                Command="{Binding GenerateLargeSampleCommand}"
+                <TextBlock Text="{l:Loc Parse.LargeSample}" />
-                ToolTip.Tip="Generate 50 000 rows, so progress and cancellation are observable"
-              >
-                <TextBlock Text="50k rows" />
               </Button>
 
-              <Button Classes="icon" Command="{Binding ClearCommand}" ToolTip.Tip="Clear input and results">
+              <Button Classes="icon" Command="{Binding ClearCommand}" ToolTip.Tip="{l:Loc Parse.ClearTip}">
                 <PathIcon Classes="glyph" Data="{DynamicResource IconBroom}" />
               </Button>
             </StackPanel>
@@ -94,7 +92,7 @@
             BorderThickness="0,0,0,1"
             BorderBrush="{DynamicResource AppBorderBrush}"
           >
-            <TextBlock Classes="caption" Text="INPUT" />
+            <TextBlock Classes="caption" Text="{l:Loc Parse.Input}" />
           </Border>
           <TextBox
             Text="{Binding InputText}"
@@ -102,7 +100,7 @@
             VerticalContentAlignment="Top"
             AcceptsTab="True"
             TextWrapping="NoWrap"
-            PlaceholderText="Paste text here, or press Sample"
+            PlaceholderText="{l:Loc Parse.InputPlaceholder}"
             BorderThickness="0"
             Background="Transparent"
             FontFamily="Cascadia Code,Consolas,Menlo,DejaVu Sans Mono,monospace"
@@ -125,7 +123,7 @@
               BorderBrush="{DynamicResource AppBorderBrush}"
             >
               <StackPanel Orientation="Horizontal" Spacing="8">
-                <TextBlock Classes="caption" Text="RECORDS" VerticalAlignment="Center" />
+                <TextBlock Classes="caption" Text="{l:Loc Parse.Records}" VerticalAlignment="Center" />
                 <Border Classes="chip">
                   <TextBlock Classes="mono caption" Text="{Binding Records.Count}" />
                 </Border>
@@ -190,7 +188,7 @@
                   Foreground="{DynamicResource AppDangerBrush}"
                   VerticalAlignment="Center"
                 />
-                <TextBlock Classes="caption" Text="ERRORS" VerticalAlignment="Center" />
+                <TextBlock Classes="caption" Text="{l:Loc Parse.Errors}" VerticalAlignment="Center" />
                 <Border Classes="chip danger">
                   <TextBlock Classes="mono caption" Text="{Binding Errors.Count}" />
                 </Border>
@@ -199,12 +197,12 @@
 
             <ListBox ItemsSource="{Binding Errors}" Background="Transparent" BorderThickness="0">
               <ListBox.ItemTemplate>
-                <DataTemplate x:DataType="parsing:ParseError">
+                <DataTemplate x:DataType="vm:ParseErrorViewModel">
                   <StackPanel Orientation="Horizontal" Spacing="10">
                     <Border Classes="chip danger" VerticalAlignment="Center" MinWidth="44">
                       <TextBlock Classes="mono caption" Text="{Binding LineNumber}" HorizontalAlignment="Center" />
                     </Border>
-                    <TextBlock Classes="muted" Text="{Binding Message}" VerticalAlignment="Center" />
+                    <TextBlock Classes="muted" Text="{Binding Text}" VerticalAlignment="Center" />
                   </StackPanel>
                 </DataTemplate>
               </ListBox.ItemTemplate>

src/AvParser.UI/Views/ProxiesView.axaml

@@ -1,53 +1,62 @@
 <UserControl
   xmlns="https://github.com/avaloniaui"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+  xmlns:l="clr-namespace:AvParser.UI.Localization"
   xmlns:vm="clr-namespace:AvParser.UI.ViewModels"
   xmlns:conv="clr-namespace:AvParser.UI.Converters"
   x:Class="AvParser.UI.Views.ProxiesView"
   x:DataType="vm:ProxiesViewModel"
 >
+  <UserControl.Resources>
+    <DataTemplate x:Key="LocalizedOptionTemplate" x:DataType="l:LocalizedOption">
+      <TextBlock Text="{Binding Label}" />
+    </DataTemplate>
+  </UserControl.Resources>
+
   <Grid RowDefinitions="Auto,Auto,*">
     <!-- ===== Toolbar ===== -->
     <Border Grid.Row="0" Classes="card" Margin="0,0,0,12">
       <StackPanel Spacing="12">
         <WrapPanel Orientation="Horizontal">
           <StackPanel Spacing="4" Margin="0,0,16,8">
-            <TextBlock Classes="caption" Text="POOL" />
+            <TextBlock Classes="caption" Text="{l:Loc Proxies.Pool}" />
             <StackPanel Orientation="Horizontal" Spacing="8">
-              <Button Classes="primary" Command="{Binding RefreshCommand}" ToolTip.Tip="Reload every source">
+              <Button Classes="primary" Command="{Binding RefreshCommand}" ToolTip.Tip="{l:Loc Proxies.RefreshTip}">
                 <StackPanel Orientation="Horizontal" Spacing="8">
                   <PathIcon Classes="glyph" Data="{DynamicResource IconRefresh}" />
-                  <TextBlock Text="Refresh" />
+                  <TextBlock Text="{l:Loc Proxies.Refresh}" />
                 </StackPanel>
               </Button>
-              <Button Command="{Binding SweepCommand}" ToolTip.Tip="Probe every proxy in the pool">
+              <Button Command="{Binding SweepCommand}" ToolTip.Tip="{l:Loc Proxies.CheckAllTip}">
                 <StackPanel Orientation="Horizontal" Spacing="8">
                   <PathIcon Classes="glyph" Data="{DynamicResource IconShield}" />
-                  <TextBlock Text="Check all" />
+                  <TextBlock Text="{l:Loc Proxies.CheckAll}" />
                 </StackPanel>
               </Button>
             </StackPanel>
           </StackPanel>
 
           <StackPanel Spacing="4" Margin="0,0,16,8" MinWidth="220">
-            <TextBlock Classes="caption" Text="SEARCH" />
+            <TextBlock Classes="caption" Text="{l:Loc Proxies.Search}" />
-            <TextBox Text="{Binding SearchText}" PlaceholderText="address or country" />
+            <TextBox Text="{Binding SearchText}" PlaceholderText="{l:Loc Proxies.SearchPlaceholder}" />
           </StackPanel>
 
           <StackPanel Spacing="4" Margin="0,0,16,8" MinWidth="130">
-            <TextBlock Classes="caption" Text="PROTOCOL" />
+            <TextBlock Classes="caption" Text="{l:Loc Proxies.Protocol}" />
             <ComboBox
               ItemsSource="{Binding ProtocolFilters}"
               SelectedItem="{Binding ProtocolFilter}"
+              ItemTemplate="{StaticResource LocalizedOptionTemplate}"
               HorizontalAlignment="Stretch"
             />
           </StackPanel>
 
           <StackPanel Spacing="4" Margin="0,0,16,8" MinWidth="130">
-            <TextBlock Classes="caption" Text="STATUS" />
+            <TextBlock Classes="caption" Text="{l:Loc Proxies.StatusColumn}" />
             <ComboBox
               ItemsSource="{Binding HealthFilters}"
               SelectedItem="{Binding HealthFilter}"
+              ItemTemplate="{StaticResource LocalizedOptionTemplate}"
               HorizontalAlignment="Stretch"
             />
           </StackPanel>
@@ -57,19 +66,19 @@
           <Border Classes="chip accent">
             <TextBlock Classes="mono caption">
               <Run Text="{Binding AliveCount}" />
-              <Run Text="alive" />
+              <Run Text="{l:Loc Proxies.Alive}" />
             </TextBlock>
           </Border>
           <Border Classes="chip">
             <TextBlock Classes="mono caption">
               <Run Text="{Binding TotalCount}" />
-              <Run Text="total" />
+              <Run Text="{l:Loc Proxies.Total}" />
             </TextBlock>
           </Border>
           <Border Classes="chip">
             <TextBlock Classes="mono caption">
               <Run Text="{Binding MatchedCount}" />
-              <Run Text="matched" />
+              <Run Text="{l:Loc Proxies.Matched}" />
             </TextBlock>
           </Border>
         </StackPanel>
@@ -102,7 +111,7 @@
             BorderThickness="0,0,0,1"
             BorderBrush="{DynamicResource AppBorderBrush}"
           >
-            <TextBlock Classes="caption" Text="PROXIES" />
+            <TextBlock Classes="caption" Text="{l:Loc Proxies.ListHeader}" />
           </Border>
 
           <ListBox
@@ -173,7 +182,7 @@
             BorderThickness="0,0,0,1"
             BorderBrush="{DynamicResource AppBorderBrush}"
           >
-            <TextBlock Classes="caption" Text="CUSTOM PROXIES" />
+            <TextBlock Classes="caption" Text="{l:Loc Proxies.CustomHeader}" />
           </Border>
 
           <StackPanel DockPanel.Dock="Bottom" Spacing="8" Margin="16,12">
@@ -181,24 +190,21 @@
               <Button Classes="primary" Command="{Binding AddCustomCommand}">
                 <StackPanel Orientation="Horizontal" Spacing="8">
                   <PathIcon Classes="glyph" Data="{DynamicResource IconPlus}" />
-                  <TextBlock Text="Add" />
+                  <TextBlock Text="{l:Loc Proxies.Add}" />
                 </StackPanel>
               </Button>
               <Button
                 Classes="destructive"
                 Command="{Binding RemoveSelectedCommand}"
-                ToolTip.Tip="Remove the selected custom proxy"
+                ToolTip.Tip="{l:Loc Proxies.RemoveTip}"
               >
-                <TextBlock Text="Remove" />
+                <TextBlock Text="{l:Loc Proxies.Remove}" />
               </Button>
-              <Button Classes="icon" Command="{Binding ClearCustomCommand}" ToolTip.Tip="Clear the custom list">
+              <Button Classes="icon" Command="{Binding ClearCustomCommand}" ToolTip.Tip="{l:Loc Proxies.ClearTip}">
                 <PathIcon Classes="glyph" Data="{DynamicResource IconTrash}" />
               </Button>
             </StackPanel>
-            <TextBlock
+            <TextBlock Classes="muted" Text="{l:Loc Proxies.CustomHint}" />
-              Classes="muted"
-              Text="One per line. scheme://host:port, or host:port for plain HTTP. user:pass@ is supported."
-            />
           </StackPanel>
 
           <TextBox

src/AvParser.UI/Views/SettingsView.axaml

@@ -1,51 +1,72 @@
 <UserControl
   xmlns="https://github.com/avaloniaui"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+  xmlns:l="clr-namespace:AvParser.UI.Localization"
   xmlns:vm="clr-namespace:AvParser.UI.ViewModels"
   x:Class="AvParser.UI.Views.SettingsView"
   x:DataType="vm:SettingsViewModel"
 >
+  <UserControl.Resources>
+    <!-- Every picker on this page holds LocalizedOption values; the non-generic base is what
+         lets a compiled binding name a data type here. -->
+    <DataTemplate x:Key="LocalizedOptionTemplate" x:DataType="l:LocalizedOption">
+      <TextBlock Text="{Binding Label}" />
+    </DataTemplate>
+  </UserControl.Resources>
+
   <ScrollViewer>
     <StackPanel Spacing="16" MaxWidth="720" HorizontalAlignment="Left">
       <Border Classes="card">
         <StackPanel Spacing="16">
-          <TextBlock Classes="subtitle" Text="Appearance" />
+          <TextBlock Classes="subtitle" Text="{l:Loc Settings.Appearance}" />
 
           <StackPanel Spacing="6">
-            <TextBlock Classes="caption" Text="THEME" />
+            <TextBlock Classes="caption" Text="{l:Loc Settings.Theme}" />
             <ComboBox
               ItemsSource="{Binding Themes}"
               SelectedItem="{Binding SelectedTheme}"
+              ItemTemplate="{StaticResource LocalizedOptionTemplate}"
               HorizontalAlignment="Stretch"
             />
-            <TextBlock Classes="muted" Text="System follows the operating system's light/dark setting." />
+            <TextBlock Classes="muted" Text="{l:Loc Settings.ThemeHint}" />
+          </StackPanel>
+
+          <StackPanel Spacing="6">
+            <TextBlock Classes="caption" Text="{l:Loc Settings.Language}" />
+            <ComboBox
+              ItemsSource="{Binding Languages}"
+              SelectedItem="{Binding SelectedLanguage}"
+              ItemTemplate="{StaticResource LocalizedOptionTemplate}"
+              HorizontalAlignment="Stretch"
+            />
+            <TextBlock Classes="muted" Text="{l:Loc Settings.LanguageHint}" />
           </StackPanel>
         </StackPanel>
       </Border>
 
       <Border Classes="card">
         <StackPanel Spacing="16">
-          <TextBlock Classes="subtitle" Text="Diagnostics" />
+          <TextBlock Classes="subtitle" Text="{l:Loc Settings.Diagnostics}" />
 
           <StackPanel Spacing="6">
-            <TextBlock Classes="caption" Text="MINIMUM LOG LEVEL" />
+            <TextBlock Classes="caption" Text="{l:Loc Settings.LogLevel}" />
             <ComboBox
               ItemsSource="{Binding LogLevels}"
               SelectedItem="{Binding SelectedLogLevel}"
               HorizontalAlignment="Stretch"
             />
-            <TextBlock Classes="muted" Text="Applies immediately — no restart needed." />
+            <TextBlock Classes="muted" Text="{l:Loc Settings.LogLevelHint}" />
           </StackPanel>
 
           <Separator Classes="section" />
 
           <StackPanel Spacing="6">
-            <TextBlock Classes="caption" Text="SETTINGS FILE" />
+            <TextBlock Classes="caption" Text="{l:Loc Settings.SettingsFile}" />
             <SelectableTextBlock Classes="mono" Text="{Binding SettingsFile}" TextWrapping="Wrap" />
           </StackPanel>
 
           <StackPanel Spacing="6">
-            <TextBlock Classes="caption" Text="LOG DIRECTORY" />
+            <TextBlock Classes="caption" Text="{l:Loc Settings.LogDirectory}" />
             <SelectableTextBlock Classes="mono" Text="{Binding LogDirectory}" TextWrapping="Wrap" />
           </StackPanel>
         </StackPanel>
@@ -53,42 +74,41 @@
 
       <Border Classes="card">
         <StackPanel Spacing="16">
-          <TextBlock Classes="subtitle" Text="Proxies" />
+          <TextBlock Classes="subtitle" Text="{l:Loc Settings.Proxies}" />
 
           <StackPanel Spacing="6">
-            <TextBlock Classes="caption" Text="ROTATION" />
+            <TextBlock Classes="caption" Text="{l:Loc Settings.Rotation}" />
             <ComboBox
               ItemsSource="{Binding Rotations}"
               SelectedItem="{Binding SelectedRotation}"
+              ItemTemplate="{StaticResource LocalizedOptionTemplate}"
               HorizontalAlignment="Stretch"
             />
             <TextBlock Classes="muted" Text="{Binding RotationDescription}" />
           </StackPanel>
 
           <StackPanel Spacing="6">
-            <TextBlock Classes="caption" Text="LIVENESS CHECK" />
+            <TextBlock Classes="caption" Text="{l:Loc Settings.LivenessCheck}" />
             <ComboBox
               ItemsSource="{Binding HealthChecks}"
               SelectedItem="{Binding SelectedHealthCheck}"
+              ItemTemplate="{StaticResource LocalizedOptionTemplate}"
               HorizontalAlignment="Stretch"
             />
             <TextBlock Classes="muted" Text="{Binding HealthCheckDescription}" />
           </StackPanel>
 
-          <CheckBox IsChecked="{Binding UseProxyFeed}" Content="Use the public proxifly feed" />
+          <CheckBox IsChecked="{Binding UseProxyFeed}" Content="{l:Loc Settings.UseFeed}" />
 
           <StackPanel Spacing="6">
-            <TextBlock Classes="caption" Text="PROBE URL" />
+            <TextBlock Classes="caption" Text="{l:Loc Settings.ProbeUrl}" />
             <TextBox Text="{Binding ProxyProbeUrl}" />
-            <TextBlock
+            <TextBlock Classes="muted" Text="{l:Loc Settings.ProbeUrlHint}" />
-              Classes="muted"
-              Text="Plain HTTP by default: requiring TLS would fail every proxy that cannot do CONNECT, not just the dead ones."
-            />
           </StackPanel>
 
           <Grid ColumnDefinitions="*,16,*">
             <StackPanel Grid.Column="0" Spacing="6">
-              <TextBlock Classes="caption" Text="PROBE TIMEOUT (SEC)" />
+              <TextBlock Classes="caption" Text="{l:Loc Settings.ProbeTimeout}" />
               <NumericUpDown
                 Value="{Binding ProxyProbeTimeoutSeconds}"
                 Minimum="1"
@@ -98,7 +118,7 @@
               />
             </StackPanel>
             <StackPanel Grid.Column="2" Spacing="6">
-              <TextBlock Classes="caption" Text="PARALLEL PROBES" />
+              <TextBlock Classes="caption" Text="{l:Loc Settings.ProbeConcurrency}" />
               <NumericUpDown
                 Value="{Binding ProxyProbeConcurrency}"
                 Minimum="1"
@@ -113,34 +133,18 @@
 
       <Border Classes="card">
         <StackPanel Spacing="12">
-          <TextBlock Classes="subtitle" Text="Layout breakpoints" />
+          <TextBlock Classes="subtitle" Text="{l:Loc Settings.Breakpoints}" />
-          <TextBlock
+          <TextBlock Classes="muted" Text="{l:Loc Settings.BreakpointsHint}" />
-            Classes="muted"
-            Text="Window widths at which the navigation changes shape. Resize the window to see it happen."
-          />
 
           <Grid ColumnDefinitions="Auto,*" RowDefinitions="Auto,Auto,Auto" ColumnSpacing="16" RowSpacing="8">
-            <TextBlock Grid.Row="0" Grid.Column="0" Classes="caption" Text="COMPACT" />
+            <TextBlock Grid.Row="0" Grid.Column="0" Classes="caption" Text="{l:Loc Settings.Breakpoint.Compact}" />
-            <TextBlock Grid.Row="0" Grid.Column="1" Classes="muted">
+            <TextBlock Grid.Row="0" Grid.Column="1" Classes="muted" Text="{Binding CompactHint}" />
-              <Run Text="below" />
-              <Run Text="{Binding MediumBreakpoint}" />
-              <Run Text="px — overlay drawer" />
-            </TextBlock>
 
-            <TextBlock Grid.Row="1" Grid.Column="0" Classes="caption" Text="MEDIUM" />
+            <TextBlock Grid.Row="1" Grid.Column="0" Classes="caption" Text="{l:Loc Settings.Breakpoint.Medium}" />
-            <TextBlock Grid.Row="1" Grid.Column="1" Classes="muted">
+            <TextBlock Grid.Row="1" Grid.Column="1" Classes="muted" Text="{Binding MediumHint}" />
-              <Run Text="{Binding MediumBreakpoint}" />
-              <Run Text="–" />
-              <Run Text="{Binding ExpandedBreakpoint}" />
-              <Run Text="px — icon rail" />
-            </TextBlock>
 
-            <TextBlock Grid.Row="2" Grid.Column="0" Classes="caption" Text="EXPANDED" />
+            <TextBlock Grid.Row="2" Grid.Column="0" Classes="caption" Text="{l:Loc Settings.Breakpoint.Expanded}" />
-            <TextBlock Grid.Row="2" Grid.Column="1" Classes="muted">
+            <TextBlock Grid.Row="2" Grid.Column="1" Classes="muted" Text="{Binding ExpandedHint}" />
-              <Run Text="from" />
-              <Run Text="{Binding ExpandedBreakpoint}" />
-              <Run Text="px — full sidebar" />
-            </TextBlock>
           </Grid>
         </StackPanel>
       </Border>

src/AvParser.UI/Views/ShellView.axaml

@@ -1,6 +1,7 @@
 <rxui:ReactiveUserControl
   xmlns="https://github.com/avaloniaui"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+  xmlns:l="clr-namespace:AvParser.UI.Localization"
   xmlns:rxui="clr-namespace:ReactiveUI.Avalonia;assembly=ReactiveUI.Avalonia"
   xmlns:vm="clr-namespace:AvParser.UI.ViewModels"
   xmlns:conv="clr-namespace:AvParser.UI.Converters"
@@ -58,7 +59,7 @@
             Grid.Column="0"
             Classes="icon"
             Command="{Binding TogglePaneCommand}"
-            ToolTip.Tip="Toggle navigation"
+            ToolTip.Tip="{l:Loc Shell.ToggleNavigation}"
             Margin="0,0,4,0"
           >
             <PathIcon Classes="glyph" Data="{DynamicResource IconMenu}" />
@@ -70,7 +71,7 @@
             Classes="icon"
             Command="{Binding GoBackCommand}"
             IsVisible="{Binding CanGoBack}"
-            ToolTip.Tip="Back"
+            ToolTip.Tip="{l:Loc Shell.Back}"
             Margin="0,0,8,0"
           >
             <PathIcon Classes="glyph" Data="{DynamicResource IconBack}" />
@@ -90,7 +91,7 @@
             Grid.Column="3"
             Classes="icon"
             Command="{Binding ToggleThemeCommand}"
-            ToolTip.Tip="Switch light / dark"
+            ToolTip.Tip="{l:Loc Shell.ToggleTheme}"
           >
             <PathIcon
               Classes="glyph"

tests/AvParser.UI.HeadlessTests/Fakes.cs

@@ -14,9 +14,9 @@ namespace AvParser.UI.HeadlessTests;
 /// project: these are a few lines of trivial stand-ins, and a shared test-kit assembly would have
 /// to opt out of the <c>tests/</c> conventions (self-executing xUnit exe) to build at all.
 /// </remarks>
-internal sealed class FakePage(string title, string iconKey = "IconHome") : PageViewModel
+internal sealed class FakePage(string titleKey, string iconKey = "IconHome") : PageViewModel
 {
-    public override string Title { get; } = title;
+    public override string TitleKey { get; } = titleKey;
 
     public override string IconKey { get; } = iconKey;
 }

tests/AvParser.UI.HeadlessTests/LocalizationViewTests.cs

@@ -0,0 +1,90 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Headless.XUnit;
+using Avalonia.Threading;
+using Avalonia.VisualTree;
+using AvParser.Core.Settings;
+using AvParser.UI.Localization;
+using AvParser.UI.Navigation;
+using AvParser.UI.ViewModels;
+using AvParser.UI.Views;
+using ReactiveUI.Primitives.Concurrency;
+
+namespace AvParser.UI.HeadlessTests;
+
+public sealed class LocalizationViewTests : IDisposable
+{
+    /// <summary>Leaves the localizer where the rest of the assembly expects it.</summary>
+    public void Dispose() => Localizer.Instance.SetLanguage(AppLanguage.English);
+
+    private static (ShellView View, ShellViewModel ViewModel) ShowShell()
+    {
+        var navigation = new NavigationService([new FakePage("Page.Dashboard"), new FakePage("Page.Parse")]);
+        var viewModel = new ShellViewModel(navigation, new FakeThemeService(), ImmediateSequencer.Instance);
+        var view = new ShellView { DataContext = viewModel };
+
+        new Window
+        {
+            Width = 1400,
+            Height = 800,
+            Content = view,
+        }.Show();
+
+        Dispatcher.UIThread.RunJobs();
+        return (view, viewModel);
+    }
+
+    private static IReadOnlyList<string> RailLabels(Visual view) =>
+        [
+            .. view.GetVisualDescendants()
+                .OfType<TextBlock>()
+                .Where(block => block.Classes.Contains("navLabel"))
+                .Select(block => block.Text ?? string.Empty),
+        ];
+
+    [AvaloniaFact]
+    public void Rendered_text_follows_the_language_without_rebuilding_the_view()
+    {
+        Localizer.Instance.SetLanguage(AppLanguage.English);
+        var (view, _) = ShowShell();
+
+        var english = RailLabels(view);
+        english.ShouldBe(["Dashboard", "Parse"]);
+
+        Localizer.Instance.SetLanguage(AppLanguage.Russian);
+        Dispatcher.UIThread.RunJobs();
+
+        // The same controls, not a rebuilt tree: this is the whole point of binding through the
+        // localizer's indexer rather than resolving strings once at load.
+        RailLabels(view).ShouldBe(["Обзор", "Разбор"]);
+    }
+
+    [AvaloniaFact]
+    public void The_title_bar_follows_the_language_too()
+    {
+        Localizer.Instance.SetLanguage(AppLanguage.English);
+        var (view, viewModel) = ShowShell();
+
+        var title = view.GetVisualDescendants().OfType<TextBlock>().Single(block => block.Name == "ShellTitle");
+        title.Text.ShouldBe("Dashboard");
+
+        Localizer.Instance.SetLanguage(AppLanguage.Russian);
+        Dispatcher.UIThread.RunJobs();
+
+        viewModel.Title.ShouldBe("Обзор");
+        title.Text.ShouldBe("Обзор");
+    }
+
+    [AvaloniaFact]
+    public void Loc_markup_resolves_a_static_caption()
+    {
+        Localizer.Instance.SetLanguage(AppLanguage.Russian);
+        var (view, _) = ShowShell();
+
+        // Tooltips come from {l:Loc} rather than from a view model, so they exercise the markup
+        // extension itself.
+        var toggle = view.GetVisualDescendants().OfType<Button>().Single(button => button.Name == "PaneToggle");
+
+        ToolTip.GetTip(toggle).ShouldBe("Показать или скрыть навигацию");
+    }
+}

tests/AvParser.UI.HeadlessTests/ShellViewTests.cs

@@ -5,6 +5,7 @@ using Avalonia.Styling;
 using Avalonia.Threading;
 using Avalonia.VisualTree;
 using AvParser.Core.Settings;
+using AvParser.UI.Localization;
 using AvParser.UI.Navigation;
 using AvParser.UI.Responsive;
 using AvParser.UI.Services;
@@ -27,7 +28,10 @@ public class ShellViewTests
     /// </remarks>
     private static (ShellView View, ShellViewModel ViewModel, Window Window) ShowShell(double width)
     {
-        var navigation = new NavigationService([new FakePage("First"), new FakePage("Second", "IconDocument")]);
+        var navigation = new NavigationService([
+            new FakePage("Page.Dashboard"),
+            new FakePage("Page.Parse", "IconDocument"),
+        ]);
 
         // ImmediateSequencer, not the real main-thread one: derived properties then settle within
         // the same layout pass, so a single RunJobs() is enough for the bindings to catch up.
@@ -108,7 +112,7 @@ public class ShellViewTests
 
         var host = view.GetVisualDescendants().OfType<TransitioningContentControl>().Single();
         host.Content.ShouldBeSameAs(second);
-        viewModel.Title.ShouldBe("Second");
+        viewModel.Title.ShouldBe(Localizer.Instance["Page.Parse"]);
     }
 
     /// <summary>

tests/AvParser.UI.Tests/Fakes/FakePage.cs

@@ -3,9 +3,13 @@ using AvParser.UI.ViewModels;
 namespace AvParser.UI.Tests.Fakes;
 
 /// <summary>A navigation destination with no behaviour, for exercising the shell and the stack.</summary>
-internal sealed class FakePage(string title, string iconKey = "IconHome") : PageViewModel
+/// <remarks>
+/// Takes a real resource key rather than a literal caption, so the tests exercise the same
+/// lookup the app does instead of a special case that would hide a broken key.
+/// </remarks>
+internal sealed class FakePage(string titleKey, string iconKey = "IconHome") : PageViewModel
 {
-    public override string Title { get; } = title;
+    public override string TitleKey { get; } = titleKey;
 
     public override string IconKey { get; } = iconKey;
 }
@@ -13,7 +17,7 @@ internal sealed class FakePage(string title, string iconKey = "IconHome") : Page
 /// <summary>A second page type, so <c>NavigateTo&lt;TPage&gt;()</c> has something to discriminate on.</summary>
 internal sealed class OtherFakePage : PageViewModel
 {
-    public override string Title => "Other";
+    public override string TitleKey => "Page.About";
 
     public override string IconKey => "IconInfo";
 }

tests/AvParser.UI.Tests/LocalizationTests.cs

@@ -0,0 +1,221 @@
+using System.Globalization;
+using System.Resources;
+using System.Text.RegularExpressions;
+using AvParser.Core.Settings;
+using AvParser.UI.Localization;
+
+namespace AvParser.UI.Tests;
+
+public sealed class LocalizationTests : IDisposable
+{
+    private static readonly CultureInfo English = CultureInfo.GetCultureInfo("en");
+    private static readonly CultureInfo Russian = CultureInfo.GetCultureInfo("ru");
+
+    private static readonly ResourceManager Resources = new(
+        "AvParser.UI.Localization.Strings",
+        typeof(Localizer).Assembly
+    );
+
+    /// <summary>Leaves the localizer where the rest of the suite expects it.</summary>
+    public void Dispose() => Localizer.Instance.SetLanguage(AppLanguage.English);
+
+    /// <summary>
+    /// Reads one language's resources without letting it fall back to another.
+    /// </summary>
+    /// <remarks>
+    /// English lives in the neutral <c>Strings.resx</c>, which resolves under the invariant
+    /// culture rather than under "en". <c>tryParents: false</c> matters: with fallback on, a
+    /// missing Russian satellite would quietly serve English and every comparison below would
+    /// pass while the app shipped untranslated.
+    /// </remarks>
+    private static IReadOnlyDictionary<string, string> Read(CultureInfo culture)
+    {
+        var lookup = Equals(culture, English) ? CultureInfo.InvariantCulture : culture;
+
+        // Deliberately not disposed: ResourceManager hands back a cached instance, and disposing
+        // it breaks every later read in the assembly.
+        var set = Resources.GetResourceSet(lookup, createIfNotExists: true, tryParents: false);
+        set.ShouldNotBeNull();
+
+        return set.Cast<System.Collections.DictionaryEntry>()
+            .ToDictionary(
+                entry => (string)entry.Key,
+                entry => (string?)entry.Value ?? string.Empty,
+                StringComparer.Ordinal
+            );
+    }
+
+    [Fact]
+    public void Russian_translates_every_english_key()
+    {
+        var english = Read(English);
+        var russian = Read(Russian);
+
+        english.ShouldNotBeEmpty();
+        russian.Keys.Except(english.Keys, StringComparer.Ordinal).ShouldBeEmpty("Russian has keys English does not");
+        english.Keys.Except(russian.Keys, StringComparer.Ordinal).ShouldBeEmpty("Russian is missing keys");
+    }
+
+    [Fact]
+    public void No_translation_is_blank() =>
+        Read(Russian).Where(entry => string.IsNullOrWhiteSpace(entry.Value)).Select(entry => entry.Key).ShouldBeEmpty();
+
+    [Fact]
+    public void Format_placeholders_match_between_languages()
+    {
+        var english = Read(English);
+        var russian = Read(Russian);
+
+        // A translation that drops a {0} throws at runtime rather than merely reading oddly, so
+        // the placeholder sets have to be identical.
+        var mismatched = english
+            .Where(entry => Placeholders(entry.Value) != Placeholders(russian[entry.Key]))
+            .Select(entry => entry.Key)
+            .ToArray();
+
+        mismatched.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void Every_plural_key_has_all_three_forms()
+    {
+        var english = Read(English);
+
+        // Russian needs One/Few/Many; a family missing one of them would silently render "!key!".
+        var families = english
+            .Keys.Where(key => key.EndsWith(".One", StringComparison.Ordinal))
+            .Select(key => key[..^4])
+            .ToArray();
+
+        families.ShouldNotBeEmpty();
+
+        foreach (var family in families)
+        {
+            foreach (var suffix in new[] { "One", "Few", "Many" })
+            {
+                english.ShouldContainKey($"{family}.{suffix}");
+            }
+        }
+    }
+
+    [Theory]
+    [InlineData(1, "One")]
+    [InlineData(2, "Few")]
+    [InlineData(4, "Few")]
+    [InlineData(5, "Many")]
+    [InlineData(11, "Many")]
+    [InlineData(12, "Many")]
+    [InlineData(14, "Many")]
+    [InlineData(21, "One")]
+    [InlineData(22, "Few")]
+    [InlineData(25, "Many")]
+    [InlineData(101, "One")]
+    [InlineData(111, "Many")]
+    [InlineData(0, "Many")]
+    public void Russian_plural_rules(int count, string expected) =>
+        Localizer.SuffixFor(count, Russian).ShouldBe(expected);
+
+    [Theory]
+    [InlineData(0, "Many")]
+    [InlineData(1, "One")]
+    [InlineData(2, "Many")]
+    [InlineData(21, "Many")]
+    public void English_plural_rules(int count, string expected) =>
+        Localizer.SuffixFor(count, English).ShouldBe(expected);
+
+    [Fact]
+    public void Plural_lookup_picks_the_right_form()
+    {
+        Localizer.Instance.SetLanguage(AppLanguage.Russian);
+
+        Localizer.Instance.Plural("Parse.Count.Records", 1).ShouldBe("1 запись");
+        Localizer.Instance.Plural("Parse.Count.Records", 3).ShouldBe("3 записи");
+        Localizer.Instance.Plural("Parse.Count.Records", 7).ShouldBe("7 записей");
+    }
+
+    [Fact]
+    public void Switching_language_changes_what_lookups_return()
+    {
+        Localizer.Instance.SetLanguage(AppLanguage.English);
+        var english = Localizer.Instance["Page.Settings"];
+
+        Localizer.Instance.SetLanguage(AppLanguage.Russian);
+
+        Localizer.Instance["Page.Settings"].ShouldNotBe(english);
+        Localizer.Instance["Page.Settings"].ShouldBe("Настройки");
+    }
+
+    [Fact]
+    public void Switching_language_invalidates_bindings()
+    {
+        Localizer.Instance.SetLanguage(AppLanguage.English);
+
+        var notifications = new List<string?>();
+        void Handler(object? sender, System.ComponentModel.PropertyChangedEventArgs e) =>
+            notifications.Add(e.PropertyName);
+
+        Localizer.Instance.PropertyChanged += Handler;
+        try
+        {
+            Localizer.Instance.SetLanguage(AppLanguage.Russian);
+        }
+        finally
+        {
+            Localizer.Instance.PropertyChanged -= Handler;
+        }
+
+        // "Item[]" is what makes every {l:Loc} binding re-read; without it the UI would keep the
+        // previous language until it was rebuilt.
+        notifications.ShouldContain("Item[]");
+    }
+
+    [Fact]
+    public void Setting_the_same_language_twice_does_not_churn_bindings()
+    {
+        Localizer.Instance.SetLanguage(AppLanguage.Russian);
+
+        var raised = 0;
+        void Handler(object? sender, System.ComponentModel.PropertyChangedEventArgs e) => raised++;
+
+        Localizer.Instance.PropertyChanged += Handler;
+        try
+        {
+            Localizer.Instance.SetLanguage(AppLanguage.Russian);
+        }
+        finally
+        {
+            Localizer.Instance.PropertyChanged -= Handler;
+        }
+
+        raised.ShouldBe(0);
+    }
+
+    [Fact]
+    public void An_unknown_key_is_visibly_marked() => Localizer.Instance["No.Such.Key"].ShouldBe("!No.Such.Key!");
+
+    [Fact]
+    public void A_fallback_is_used_when_a_key_is_absent() =>
+        Localizer.Instance.GetOrDefault("Parser.brand-new.Name", "Brand new").ShouldBe("Brand new");
+
+    [Theory]
+    [InlineData(AppLanguage.English, "en")]
+    [InlineData(AppLanguage.Russian, "ru")]
+    public void Explicit_languages_map_to_their_culture(AppLanguage language, string expected) =>
+        AppLanguages.ToCulture(language).TwoLetterISOLanguageName.ShouldBe(expected);
+
+    [Theory]
+    [InlineData("ru-RU", "ru")]
+    [InlineData("ru", "ru")]
+    [InlineData("en-GB", "en")]
+    [InlineData("de-DE", "en")]
+    [InlineData("ja-JP", "en")]
+    public void System_follows_the_os_only_where_a_translation_exists(string system, string expected) =>
+        // A half-translated German would be worse than plain English, so anything unsupported
+        // lands on English rather than on the OS language.
+        AppLanguages
+            .ToCulture(AppLanguage.System, CultureInfo.GetCultureInfo(system))
+            .TwoLetterISOLanguageName.ShouldBe(expected);
+
+    private static string Placeholders(string value) =>
+        string.Concat(Regex.Matches(value, @"\{\d+\}").Select(match => match.Value).Order());
+}

tests/AvParser.UI.Tests/ProxiesViewModelTests.cs

@@ -84,7 +84,7 @@ public class ProxiesViewModelTests
         );
 
         await Run(page.RefreshCommand);
-        page.ProtocolFilter = ProxyProtocolFilter.Socks5;
+        page.ProtocolFilter = page.ProtocolFilters.Single(option => option.Value == ProxyProtocolFilter.Socks5);
         await Task.Delay(250, TestContext.Current.CancellationToken);
 
         page.Proxies.ShouldHaveSingleItem().Protocol.ShouldBe("SOCKS5");

tests/AvParser.UI.Tests/ShellViewModelTests.cs

@@ -1,5 +1,6 @@
 using Avalonia.Controls;
 using AvParser.Core.Settings;
+using AvParser.UI.Localization;
 using AvParser.UI.Navigation;
 using AvParser.UI.Responsive;
 using AvParser.UI.Tests.Fakes;
@@ -15,7 +16,11 @@ public class ShellViewModelTests
         AppTheme theme = AppTheme.System
     )
     {
-        var navigation = new NavigationService([new FakePage("First"), new FakePage("Second"), new OtherFakePage()]);
+        var navigation = new NavigationService([
+            new FakePage("Page.Dashboard"),
+            new FakePage("Page.Parse"),
+            new OtherFakePage(),
+        ]);
         var themeService = new FakeThemeService(theme);
 
         // ImmediateSequencer makes every derived property settle before the next line runs,
@@ -98,7 +103,7 @@ public class ShellViewModelTests
 
         navigation.Current.ShouldBeSameAs(shell.Pages[2]);
         shell.CurrentPage.ShouldBeSameAs(shell.Pages[2]);
-        shell.Title.ShouldBe("Other");
+        shell.Title.ShouldBe(Localizer.Instance["Page.About"]);
     }
 
     [Fact]