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/App.xaml.cs

@@ -14,6 +14,7 @@ using PSLauncher.Core.Downloads;
 using PSLauncher.Core.Installations;
 using PSLauncher.Core.Integrity;
 using PSLauncher.Core.Licensing;
+using PSLauncher.Core.Localization;
 using PSLauncher.Core.Manifests;
 using PSLauncher.Core.Process;
 using PSLauncher.Core.Updates;
@@ -63,6 +64,20 @@ public partial class App : Application
             "PSLauncher", "logs");
         Directory.CreateDirectory(LogsDirectory);
 
+        // Bootstrap i18n : on lit d'abord la config (sans services DI) pour fixer la
+        // langue avant que le moindre élément XAML soit instancié.
+        try
+        {
+            var bootstrapStore = new ConfigStore(
+                Microsoft.Extensions.Logging.Abstractions.NullLogger<ConfigStore>.Instance);
+            var bootstrapCfg = bootstrapStore.Load();
+            Strings.Init(bootstrapCfg.Language);
+        }
+        catch
+        {
+            Strings.Init("auto");
+        }
+
         Log.Logger = new LoggerConfiguration()
             .MinimumLevel.Debug()
             .Enrich.FromLogContext()
@@ -143,6 +158,9 @@ public partial class App : Application
 
         var window = _host.Services.GetRequiredService<MainWindow>();
         window.DataContext = _host.Services.GetRequiredService<MainViewModel>();
+        // Mise en page droite-à-gauche pour les langues RTL (arabe).
+        if (Strings.IsRightToLeft)
+            window.FlowDirection = FlowDirection.RightToLeft;
         MainWindow = window;
         window.Show();
     }