i18n: 5 languages (FR/EN/ZH/TH/AR), auto-detect from Windows + Settings picker

Localization infrastructure
---------------------------
PSLauncher.Core/Localization/Strings.cs is a static class exposing each
UI string as a static property. T(fr,en,zh,th,ar) helper switches by the
current language code. ~50 keys cover the visible top-level strings:
top bar, body, status badges, action buttons, "..." menu items, license
badge texts, Settings section headers, Onboarding dialog, Update dialog.

Bindings via x:Static in XAML:
  xmlns:loc="clr-namespace:PSLauncher.Core.Localization;assembly=PSLauncher.Core"
  Content="{x:Static loc:Strings.ActionLaunch}"

Auto-detection
--------------
LocalConfig gains a Language field defaulting to "auto". Strings.Init()
called at App.xaml.cs OnStartup before any UI:
- "auto" (or unknown code) → reads CultureInfo.CurrentUICulture
  .TwoLetterISOLanguageName, picks the matching supported language,
  falls back to English.
- explicit code → forced.
The chosen culture is then propagated to CurrentCulture / CurrentUICulture
so date/number formats follow.

Settings picker
---------------
SettingsDialog gets a top section "LANGUE" with a ComboBox bound to
SettingsViewModel.AvailableLanguages (Auto / FR / EN / ZH / TH / AR).
On Save, if the language code changed, prompt the user to confirm
restart, spawn `cmd /c timeout 1 & start PSLauncher.exe` and Shutdown
the current process — the new instance picks up the language at
bootstrap.

RTL for Arabic
--------------
Strings.IsRightToLeft is true when lang=="ar". App.xaml.cs sets
window.FlowDirection = RightToLeft on the MainWindow — WPF mirrors the
layout (icons on right, text aligned right).

Translations
------------
Done as best-effort by the assistant. The product wordmark "PROSERVE"
stays untranslated (brand). Logs and debug-level messages remain in
French in code — only user-visible UI is localized. Operator can
refine translations by editing Strings.cs and rebuilding.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/PSLauncher.App/ViewModels/SettingsViewModel.cs

@@ -13,6 +13,8 @@ using PSLauncher.Models;
 
 namespace PSLauncher.App.ViewModels;
 
+public sealed record LanguageOption(string Code, string Name);
+
 public sealed partial class SettingsViewModel : ObservableObject
 {
     private readonly IConfigStore _configStore;
@@ -29,6 +31,12 @@ public sealed partial class SettingsViewModel : ObservableObject
 
     [ObservableProperty] private string _serverBaseUrl;
     [ObservableProperty] private string _installRoot;
+    [ObservableProperty] private string _language;
+
+    public IReadOnlyList<LanguageOption> AvailableLanguages { get; } =
+        PSLauncher.Core.Localization.Strings.Available
+            .Select(t => new LanguageOption(t.Code, t.Name))
+            .ToList();
     [ObservableProperty] private string? _connectionStatus;
     [ObservableProperty] private bool _isTestingConnection;
     [ObservableProperty] private string _cacheSizeDisplay = "—";
@@ -102,6 +110,7 @@ public sealed partial class SettingsViewModel : ObservableObject
 
         _serverBaseUrl = config.ServerBaseUrl;
         _installRoot = config.InstallRoot;
+        _language = string.IsNullOrWhiteSpace(config.Language) ? "auto" : config.Language;
 
         LauncherVersion = Assembly.GetExecutingAssembly().GetName().Version?.ToString() ?? "0.0.0";
         MachineId = licenseService.GetMachineId();
@@ -201,10 +210,48 @@ public sealed partial class SettingsViewModel : ObservableObject
     [RelayCommand]
     private void Save()
     {
+        var languageChanged = !string.Equals(
+            (_config.Language ?? "auto").ToLowerInvariant(),
+            (Language ?? "auto").ToLowerInvariant(),
+            StringComparison.Ordinal);
+
         _config.ServerBaseUrl = ServerBaseUrl.TrimEnd('/');
         _config.InstallRoot = InstallRoot;
+        _config.Language = Language ?? "auto";
         _configStore.Save(_config);
-        _logger.LogInformation("Settings saved");
+        _logger.LogInformation("Settings saved (language={Lang}, changed={Changed})", _config.Language, languageChanged);
+
+        if (languageChanged)
+        {
+            // Le launcher doit être relancé pour que les bindings x:Static reflètent
+            // la nouvelle langue. Plutôt que de demander à l'utilisateur de fermer/rouvrir,
+            // on spawne un cmd qui attend la fermeture puis relance.
+            var ok = MessageBox.Show(
+                "Le launcher va redémarrer pour appliquer la nouvelle langue.",
+                "Changement de langue",
+                MessageBoxButton.OKCancel, MessageBoxImage.Information, MessageBoxResult.OK);
+            if (ok == MessageBoxResult.OK)
+            {
+                try
+                {
+                    var exe = System.Diagnostics.Process.GetCurrentProcess().MainModule?.FileName;
+                    if (!string.IsNullOrEmpty(exe))
+                    {
+                        var pid = Environment.ProcessId;
+                        var cmd = $"/c (echo Wait && timeout /t 1 /nobreak > nul) & start \"\" \"{exe}\"";
+                        Process.Start(new ProcessStartInfo
+                        {
+                            FileName = "cmd.exe",
+                            Arguments = cmd,
+                            UseShellExecute = false,
+                            CreateNoWindow = true,
+                        });
+                        Application.Current.Shutdown();
+                    }
+                }
+                catch (Exception ex) { _logger.LogError(ex, "Restart on language change failed"); }
+            }
+        }
     }
 
     [RelayCommand]