Add multilingual UI localization, modpack import/export features and multi-select

DVModManager/App.axaml.cs

@@ -24,6 +24,14 @@ public override void OnFrameworkInitializationCompleted()
         ConfigureServices(services);
         Services = services.BuildServiceProvider();
 
+        // Initialize localization service with default language (English).
+        // If settings are loaded later, the language will be updated via MainWindowViewModel.
+        // For now, we just ensure the service is ready before any UI is created.
+        var localizationService = Services.GetRequiredService<ILocalizationService>();
+        // Expose as an Application-level resource so XAML can bind to it via {StaticResource Loc}
+        Resources["Loc"] = localizationService;
+        // Language will be applied after settings load in MainWindowViewModel.InitializeAsync()
+
         // Catch unhandled exceptions on any thread and surface them in the status bar / console
         var logDir = Path.Combine(
             Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
@@ -106,6 +114,9 @@ private static void ConfigureServices(IServiceCollection services)
         // HTTP
         services.AddHttpClient();
 
+        // Localization (must be registered early, before UI/ViewModels)
+        services.AddSingleton<ILocalizationService, LocalizationService>();
+
         // Core infrastructure
         services.AddSingleton<ISettingsService, SettingsService>();
         services.AddSingleton<IDialogService, DialogService>();

DVModManager/Converters/LocalizeExtension.cs

@@ -0,0 +1,73 @@
+using System.ComponentModel;
+using Avalonia.Data;
+using Avalonia.Markup.Xaml;
+using Avalonia.Markup.Xaml.MarkupExtensions;
+using DVModManager.Services;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace DVModManager.Converters;
+
+/// <summary>
+/// Markup extension for localizing text.
+/// Usage in XAML: Text="{conv:Localize toolbar.save_profile}"
+/// </summary>
+public class LocalizeExtension : MarkupExtension
+{
+    public string Key { get; set; } = "";
+
+    public LocalizeExtension() { }
+
+    public LocalizeExtension(string key)
+    {
+        Key = key;
+    }
+
+    public override object ProvideValue(IServiceProvider serviceProvider)
+    {
+        if (string.IsNullOrWhiteSpace(Key))
+            return string.Empty;
+
+        var source = App.Services.GetRequiredService<ILocalizationService>();
+
+        // Wrap each key in a dedicated observable so PropertyChanged("Value") fires
+        // on language change — Avalonia's ReflectionBindingExtension reliably handles
+        // named-property change notifications but NOT "Item[]" (WPF/Silverlight convention).
+        var localizedValue = new LocalizedValue(source, Key);
+
+        var binding = new ReflectionBindingExtension(nameof(LocalizedValue.Value))
+        {
+            Source = localizedValue,
+            Mode = BindingMode.OneWay,
+            FallbackValue = Key,
+        };
+
+        return binding.ProvideValue(serviceProvider);
+    }
+}
+
+/// <summary>
+/// Single-key observable wrapper over <see cref="ILocalizationService"/>.
+/// Raises PropertyChanged("Value") whenever the active language changes,
+/// ensuring bound UI elements update immediately without relying on "Item[]".
+/// </summary>
+internal sealed class LocalizedValue : INotifyPropertyChanged
+{
+    private readonly ILocalizationService _service;
+    private readonly string _key;
+
+    public string Value => _service[_key];
+
+    public event PropertyChangedEventHandler? PropertyChanged;
+
+    public LocalizedValue(ILocalizationService service, string key)
+    {
+        _service = service;
+        _key = key;
+        service.LanguageChanged += OnLanguageChanged;
+    }
+
+    private void OnLanguageChanged(object? sender, EventArgs e)
+    {
+        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Value)));
+    }
+}

DVModManager/Converters/StringKeyConverter.cs

@@ -0,0 +1,40 @@
+using Avalonia.Data.Converters;
+using DVModManager.Services;
+
+namespace DVModManager.Converters;
+
+/// <summary>
+/// Value converter that translates a localization key (from ViewModel) to a localized string.
+/// Binding: Text="{Binding Some ObservableProperty, Converter={StaticResource LocalizeConverter}}"
+/// where the property returns a localization key like "status.activated".
+/// </summary>
+public class StringKeyConverter : IValueConverter
+{
+    public object? Convert(object? value, Type targetType, object? parameter, System.Globalization.CultureInfo culture)
+    {
+        if (value is not string key || string.IsNullOrEmpty(key))
+            return "";
+
+        try
+        {
+            var localizationService = App.Services.GetService(typeof(ILocalizationService)) as ILocalizationService;
+            if (localizationService == null)
+                return key; // Fallback
+
+            // If parameter contains format args, apply them
+            if (parameter is object[] args)
+                return localizationService.GetString(key, args);
+
+            return localizationService.GetString(key);
+        }
+        catch
+        {
+            return key;
+        }
+    }
+
+    public object? ConvertBack(object? value, Type targetType, object? parameter, System.Globalization.CultureInfo culture)
+    {
+        throw new NotImplementedException();
+    }
+}

DVModManager/DVModManager.csproj

@@ -34,4 +34,8 @@
     <AvaloniaResource Include="Assets\**" />
   </ItemGroup>
 
+  <ItemGroup>
+    <EmbeddedResource Include="Resources\strings.csv" />
+  </ItemGroup>
+
 </Project>

DVModManager/Models/AppSettings.cs

@@ -15,6 +15,9 @@ public class AppSettings
     /// <summary>"Dark" or "Light"</summary>
     public string ThemeVariant { get; set; } = "Dark";
 
+    /// <summary>Language code: "en", "de", "fr", etc.</summary>
+    public string Language { get; set; } = "en";
+
     public bool AutoCheckUpdatesOnStartup { get; set; } = true;
 
     public bool BackupBeforeChanges { get; set; } = true;