diff --git a/src/PSLauncher.App/App.xaml.cs b/src/PSLauncher.App/App.xaml.cs
index bffe8f8..7a0f1eb 100644
--- a/src/PSLauncher.App/App.xaml.cs
+++ b/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();
     }
diff --git a/src/PSLauncher.App/ViewModels/SettingsViewModel.cs b/src/PSLauncher.App/ViewModels/SettingsViewModel.cs
index e459b29..447496f 100644
--- a/src/PSLauncher.App/ViewModels/SettingsViewModel.cs
+++ b/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]
diff --git a/src/PSLauncher.App/Views/MainWindow.xaml b/src/PSLauncher.App/Views/MainWindow.xaml
index 53d62fd..8e64541 100644
--- a/src/PSLauncher.App/Views/MainWindow.xaml
+++ b/src/PSLauncher.App/Views/MainWindow.xaml
@@ -2,6 +2,7 @@
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:vm="clr-namespace:PSLauncher.App.ViewModels"
+        xmlns:loc="clr-namespace:PSLauncher.Core.Localization;assembly=PSLauncher.Core"
         xmlns:shell="clr-namespace:System.Windows.Shell;assembly=PresentationFramework"
         Title="PROSERVE Launcher"
         Icon="pack://application:,,,/Resources/favicon.ico"
@@ -113,7 +114,7 @@
                     <!-- Action button -->
                     <StackPanel Grid.Column="2" Orientation="Horizontal" VerticalAlignment="Center" Margin="12,0,0,0">
                         <Button Style="{StaticResource PrimaryButton}"
-                                Content="▶  Lancer" Padding="22,8" FontSize="13"
+                                Content="{x:Static loc:Strings.ActionLaunch}" Padding="22,8" FontSize="13"
                                 Command="{Binding LaunchCommand}"
                                 Visibility="{Binding IsInstalled, Converter={StaticResource BoolToVisibility}}" />
                         <Button Style="{StaticResource AccentButton}"
@@ -143,13 +144,13 @@
                             Click="OnMoreMenuClick">
                         <Button.ContextMenu>
                             <ContextMenu>
-                                <MenuItem Header="📜  Voir les release notes"
+                                <MenuItem Header="{x:Static loc:Strings.MenuReleaseNotes}"
                                           Command="{Binding PlacementTarget.Tag.ShowReleaseNotesCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}" />
-                                <MenuItem Header="📁  Ouvrir le dossier"
+                                <MenuItem Header="{x:Static loc:Strings.MenuOpenFolder}"
                                           Command="{Binding PlacementTarget.Tag.OpenFolderCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}"
                                           Visibility="{Binding PlacementTarget.Tag.IsInstalled, RelativeSource={RelativeSource AncestorType=ContextMenu}, Converter={StaticResource BoolToVisibility}}" />
                                 <Separator Visibility="{Binding PlacementTarget.Tag.IsInstalled, RelativeSource={RelativeSource AncestorType=ContextMenu}, Converter={StaticResource BoolToVisibility}}" />
-                                <MenuItem Header="🗑  Supprimer cette version…"
+                                <MenuItem Header="{x:Static loc:Strings.MenuUninstall}"
                                           Command="{Binding PlacementTarget.Tag.UninstallCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}"
                                           Visibility="{Binding PlacementTarget.Tag.IsInstalled, RelativeSource={RelativeSource AncestorType=ContextMenu}, Converter={StaticResource BoolToVisibility}}" />
                             </ContextMenu>
@@ -219,7 +220,7 @@
                         Cursor="Hand"
                         CornerRadius="16" Padding="14,6"
                         shell:WindowChrome.IsHitTestVisibleInChrome="True"
-                        ToolTip="Voir / changer la license">
+                        ToolTip="{x:Static loc:Strings.LicenseTooltip}">
                     <Border.Style>
                         <Style TargetType="Border">
                             <Setter Property="Background" Value="#2A1414" />
@@ -283,7 +284,7 @@
                 <StackPanel Grid.Column="2" Orientation="Horizontal"
                             HorizontalAlignment="Right" VerticalAlignment="Center">
                     <Button Style="{StaticResource SecondaryButton}"
-                            Content="⚙  Paramètres"
+                            Content="{x:Static loc:Strings.TopBarSettings}"
                             shell:WindowChrome.IsHitTestVisibleInChrome="True"
                             Command="{Binding OpenSettingsCommand}"
                             Margin="0,0,16,0" />
@@ -368,7 +369,7 @@
 
                             <!-- Label "Version courante" -->
                             <TextBlock Grid.Row="0" Grid.Column="0"
-                                       Text="VERSION COURANTE"
+                                       Text="{x:Static loc:Strings.FeaturedCurrent}"
                                        FontSize="11" FontWeight="Bold"
                                        Foreground="{StaticResource Brush.Text.Secondary}"
                                        Margin="0,0,0,4" />
@@ -412,7 +413,7 @@
                             <!-- Action principale (gros bouton) -->
                             <Button Grid.Row="0" Grid.RowSpan="3" Grid.Column="1"
                                     Style="{StaticResource PrimaryButton}"
-                                    Content="▶  LANCER"
+                                    Content="{x:Static loc:Strings.ActionLaunchBig}"
                                     FontSize="20" Padding="56,16"
                                     VerticalAlignment="Center"
                                     Command="{Binding FeaturedVersion.LaunchCommand}"
@@ -454,13 +455,13 @@
                                     Click="OnMoreMenuClick">
                                 <Button.ContextMenu>
                                     <ContextMenu>
-                                        <MenuItem Header="📜  Voir les release notes"
+                                        <MenuItem Header="{x:Static loc:Strings.MenuReleaseNotes}"
                                                   Command="{Binding PlacementTarget.Tag.ShowReleaseNotesCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}" />
-                                        <MenuItem Header="📁  Ouvrir le dossier"
+                                        <MenuItem Header="{x:Static loc:Strings.MenuOpenFolder}"
                                                   Command="{Binding PlacementTarget.Tag.OpenFolderCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}"
                                                   Visibility="{Binding PlacementTarget.Tag.IsInstalled, RelativeSource={RelativeSource AncestorType=ContextMenu}, Converter={StaticResource BoolToVisibility}}" />
                                         <Separator Visibility="{Binding PlacementTarget.Tag.IsInstalled, RelativeSource={RelativeSource AncestorType=ContextMenu}, Converter={StaticResource BoolToVisibility}}" />
-                                        <MenuItem Header="🗑  Supprimer cette version…"
+                                        <MenuItem Header="{x:Static loc:Strings.MenuUninstall}"
                                                   Command="{Binding PlacementTarget.Tag.UninstallCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}"
                                                   Visibility="{Binding PlacementTarget.Tag.IsInstalled, RelativeSource={RelativeSource AncestorType=ContextMenu}, Converter={StaticResource BoolToVisibility}}" />
                                     </ContextMenu>
@@ -477,7 +478,7 @@
                             <ColumnDefinition Width="Auto" />
                             <ColumnDefinition Width="*" />
                         </Grid.ColumnDefinitions>
-                        <TextBlock Grid.Column="0" Text="AUTRES VERSIONS"
+                        <TextBlock Grid.Column="0" Text="{x:Static loc:Strings.SectionOther}"
                                    FontSize="12" FontWeight="Bold"
                                    Foreground="{StaticResource Brush.Text.Secondary}"
                                    VerticalAlignment="Center" />
@@ -508,7 +509,7 @@
             <Button HorizontalAlignment="Left" VerticalAlignment="Bottom"
                     Margin="32,0,0,24"
                     Style="{StaticResource SecondaryButton}"
-                    Content="🔄  Vérifier les MAJ"
+                    Content="{x:Static loc:Strings.TopBarCheckUpdates}"
                     Command="{Binding CheckForUpdatesCommand}" />
 
             <!-- Copyright flottant en bas centré, sur une pill sombre pour rester
@@ -546,7 +547,7 @@
                 </StackPanel>
                 <Button Grid.Column="1"
                         Style="{StaticResource SecondaryButton}"
-                        Content="Annuler"
+                        Content="{x:Static loc:Strings.ActionCancel}"
                         VerticalAlignment="Center" Margin="12,0,0,0"
                         Command="{Binding CancelDownloadCommand}"
                         Visibility="{Binding IsBusy, Converter={StaticResource BoolToVisibility}}" />
diff --git a/src/PSLauncher.App/Views/OnboardingDialog.xaml b/src/PSLauncher.App/Views/OnboardingDialog.xaml
index fb988a4..1cd647e 100644
--- a/src/PSLauncher.App/Views/OnboardingDialog.xaml
+++ b/src/PSLauncher.App/Views/OnboardingDialog.xaml
@@ -1,7 +1,8 @@
 <Window x:Class="PSLauncher.App.Views.OnboardingDialog"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        Title="Activation PROSERVE Launcher"
+        xmlns:loc="clr-namespace:PSLauncher.Core.Localization;assembly=PSLauncher.Core"
+        Title="{x:Static loc:Strings.OnboardingTitle}"
         Icon="pack://application:,,,/Resources/favicon.ico"
         Width="540" Height="420"
         MinWidth="480" MinHeight="380"
@@ -18,17 +19,17 @@
             <RowDefinition Height="Auto" />
         </Grid.RowDefinitions>
 
-        <TextBlock Grid.Row="0" Text="Activer votre license"
+        <TextBlock Grid.Row="0" Text="{x:Static loc:Strings.OnboardingHeading}"
                    FontSize="22" FontWeight="SemiBold"
                    Foreground="{StaticResource Brush.Text.Primary}" />
 
         <TextBlock Grid.Row="1"
-                   Text="Saisis la clé fournie par ASTERION. Elle te donne accès aux téléchargements jusqu'à la date de validité associée."
+                   Text="{x:Static loc:Strings.OnboardingBody}"
                    TextWrapping="Wrap"
                    Foreground="{StaticResource Brush.Text.Secondary}"
                    Margin="0,8,0,18" />
 
-        <TextBlock Grid.Row="2" Text="Clé de license"
+        <TextBlock Grid.Row="2" Text="{x:Static loc:Strings.OnboardingLicenseKey}"
                    FontSize="12" FontWeight="Bold"
                    Foreground="{StaticResource Brush.Text.Secondary}" />
         <TextBox  Grid.Row="3" x:Name="KeyBox"
@@ -52,12 +53,12 @@
 
         <StackPanel Grid.Row="5" Orientation="Horizontal" HorizontalAlignment="Right" Margin="0,18,0,0">
             <Button Style="{StaticResource SecondaryButton}"
-                    Content="Plus tard"
+                    Content="{x:Static loc:Strings.ActionLater}"
                     IsCancel="True"
                     Margin="0,0,12,0"
                     Click="OnLater" />
             <Button Style="{StaticResource AccentButton}"
-                    Content="Activer"
+                    Content="{x:Static loc:Strings.OnboardingActivate}"
                     Padding="32,10"
                     IsDefault="True"
                     Click="OnActivate"
diff --git a/src/PSLauncher.App/Views/SettingsDialog.xaml b/src/PSLauncher.App/Views/SettingsDialog.xaml
index 5f79dba..ae745ed 100644
--- a/src/PSLauncher.App/Views/SettingsDialog.xaml
+++ b/src/PSLauncher.App/Views/SettingsDialog.xaml
@@ -2,7 +2,8 @@
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:vm="clr-namespace:PSLauncher.App.ViewModels"
-        Title="Paramètres"
+        xmlns:loc="clr-namespace:PSLauncher.Core.Localization;assembly=PSLauncher.Core"
+        Title="{x:Static loc:Strings.SettingsTitle}"
         Icon="pack://application:,,,/Resources/favicon.ico"
         Width="640" Height="720"
         MinWidth="540" MinHeight="500"
@@ -22,13 +23,36 @@
 
         <!-- Header -->
         <Border Grid.Row="0" Padding="32,24,32,16">
-            <TextBlock Text="Paramètres" FontSize="22" FontWeight="SemiBold"
+            <TextBlock Text="{x:Static loc:Strings.SettingsTitle}" FontSize="22" FontWeight="SemiBold"
                        Foreground="{StaticResource Brush.Text.Primary}" />
         </Border>
 
         <ScrollViewer Grid.Row="1" VerticalScrollBarVisibility="Auto" Padding="32,0,32,16">
             <StackPanel>
 
+                <!-- Langue de l'interface -->
+                <Border Background="{StaticResource Brush.Bg.Card}"
+                        BorderBrush="{StaticResource Brush.Border}" BorderThickness="1"
+                        CornerRadius="6" Padding="20" Margin="0,0,0,16">
+                    <StackPanel>
+                        <TextBlock Text="{x:Static loc:Strings.SettingsLanguage}"
+                                   FontSize="11" FontWeight="Bold"
+                                   Foreground="{StaticResource Brush.Text.Secondary}"
+                                   Margin="0,0,0,8" />
+                        <ComboBox ItemsSource="{Binding AvailableLanguages}"
+                                  DisplayMemberPath="Name"
+                                  SelectedValuePath="Code"
+                                  SelectedValue="{Binding Language, Mode=TwoWay}"
+                                  Background="#1A1A20"
+                                  Foreground="{StaticResource Brush.Text.Primary}"
+                                  BorderBrush="{StaticResource Brush.Border}"
+                                  BorderThickness="1" Padding="8" />
+                        <TextBlock Text="{x:Static loc:Strings.SettingsLanguageHint}"
+                                   FontSize="11" Foreground="{StaticResource Brush.Text.Secondary}"
+                                   FontStyle="Italic" Margin="0,6,0,0" TextWrapping="Wrap" />
+                    </StackPanel>
+                </Border>
+
                 <!-- License (en tête, bordure colorée selon état) -->
                 <Border BorderThickness="2"
                         CornerRadius="6" Padding="20" Margin="0,0,0,16">
@@ -83,7 +107,7 @@
 
                         <!-- Header text -->
                         <TextBlock Grid.Row="0" Grid.Column="1"
-                                   Text="LICENSE"
+                                   Text="{x:Static loc:Strings.SettingsLicense}"
                                    FontSize="11" FontWeight="Bold"
                                    Foreground="{StaticResource Brush.Text.Secondary}" />
                         <TextBlock Grid.Row="1" Grid.Column="1"
@@ -121,7 +145,7 @@
                         BorderBrush="{StaticResource Brush.Border}" BorderThickness="1"
                         CornerRadius="6" Padding="20" Margin="0,0,0,16">
                     <StackPanel>
-                        <TextBlock Text="SERVEUR"
+                        <TextBlock Text="{x:Static loc:Strings.SettingsServer}"
                                    FontSize="11" FontWeight="Bold"
                                    Foreground="{StaticResource Brush.Text.Secondary}"
                                    Margin="0,0,0,8" />
@@ -141,7 +165,7 @@
                                      BorderThickness="1" Padding="8" />
                             <Button Grid.Column="1" Margin="8,0,0,0"
                                     Style="{StaticResource SecondaryButton}"
-                                    Content="Tester"
+                                    Content="{x:Static loc:Strings.SettingsTest}"
                                     Command="{Binding TestConnectionCommand}"
                                     IsEnabled="{Binding IsTestingConnection, Converter={StaticResource InverseBoolToBool}}" />
                         </Grid>
@@ -156,7 +180,7 @@
                         BorderBrush="{StaticResource Brush.Border}" BorderThickness="1"
                         CornerRadius="6" Padding="20" Margin="0,0,0,16">
                     <StackPanel>
-                        <TextBlock Text="INSTALLATION"
+                        <TextBlock Text="{x:Static loc:Strings.SettingsInstallation}"
                                    FontSize="11" FontWeight="Bold"
                                    Foreground="{StaticResource Brush.Text.Secondary}"
                                    Margin="0,0,0,8" />
@@ -177,7 +201,7 @@
                                      FontFamily="Consolas" />
                             <Button Grid.Column="1" Margin="8,0,0,0"
                                     Style="{StaticResource SecondaryButton}"
-                                    Content="📁  Parcourir"
+                                    Content="{x:Static loc:Strings.SettingsBrowse}"
                                     Command="{Binding BrowseInstallRootCommand}" />
                         </Grid>
                     </StackPanel>
@@ -188,7 +212,7 @@
                         BorderBrush="{StaticResource Brush.Border}" BorderThickness="1"
                         CornerRadius="6" Padding="20" Margin="0,0,0,16">
                     <StackPanel>
-                        <TextBlock Text="CACHE DE TÉLÉCHARGEMENTS"
+                        <TextBlock Text="{x:Static loc:Strings.SettingsCache}"
                                    FontSize="11" FontWeight="Bold"
                                    Foreground="{StaticResource Brush.Text.Secondary}"
                                    Margin="0,0,0,8" />
@@ -215,7 +239,7 @@
                                     Command="{Binding OpenCacheFolderCommand}" />
                             <Button Grid.Column="2" Margin="8,0,0,0"
                                     Style="{StaticResource SecondaryButton}"
-                                    Content="🗑  Vider"
+                                    Content="{x:Static loc:Strings.SettingsClearCache}"
                                     Command="{Binding ClearCacheCommand}" />
                         </Grid>
                     </StackPanel>
@@ -226,7 +250,7 @@
                         BorderBrush="{StaticResource Brush.Border}" BorderThickness="1"
                         CornerRadius="6" Padding="20" Margin="0,0,0,16">
                     <StackPanel>
-                        <TextBlock Text="LOGS &amp; APPLICATION"
+                        <TextBlock Text="{x:Static loc:Strings.SettingsLogs}"
                                    FontSize="11" FontWeight="Bold"
                                    Foreground="{StaticResource Brush.Text.Secondary}"
                                    Margin="0,0,0,8" />
@@ -271,12 +295,12 @@
                 Padding="20,12">
             <StackPanel Orientation="Horizontal" HorizontalAlignment="Right">
                 <Button Style="{StaticResource SecondaryButton}"
-                        Content="Annuler"
+                        Content="{x:Static loc:Strings.ActionCancel}"
                         IsCancel="True"
                         Margin="0,0,12,0"
                         Click="OnCancel" />
                 <Button Style="{StaticResource AccentButton}"
-                        Content="Enregistrer"
+                        Content="{x:Static loc:Strings.ActionSave}"
                         Padding="32,8"
                         IsDefault="True"
                         Click="OnSave" />
diff --git a/src/PSLauncher.Core/Localization/Strings.cs b/src/PSLauncher.Core/Localization/Strings.cs
new file mode 100644
index 0000000..c9ff8b5
--- /dev/null
+++ b/src/PSLauncher.Core/Localization/Strings.cs
@@ -0,0 +1,155 @@
+using System.Globalization;
+
+namespace PSLauncher.Core.Localization;
+
+/// <summary>
+/// Strings localisés du launcher. Approche statique : la langue est résolue au
+/// startup (auto-détection ou setting utilisateur) puis fixée pour toute la
+/// session. Tout changement de langue nécessite un redémarrage du launcher
+/// (les bindings XAML x:Static ne refresh pas dynamiquement).
+///
+/// Langues supportées : fr (par défaut), en, zh (Simplified), th, ar.
+/// Pour Arabic, FlowDirection doit aussi être basculé en RTL côté Window.
+/// </summary>
+public static class Strings
+{
+    private static string _lang = "fr";
+
+    /// <summary>Code ISO 639-1 (2 lettres) actuellement actif.</summary>
+    public static string Lang => _lang;
+
+    /// <summary>True quand la langue actuelle s'écrit de droite à gauche.</summary>
+    public static bool IsRightToLeft => _lang == "ar";
+
+    /// <summary>Langues proposées au sélecteur des Settings (code → libellé natif).</summary>
+    public static readonly (string Code, string Name)[] Available =
+    {
+        ("auto", "Automatique (langue du système)"),
+        ("fr",   "Français"),
+        ("en",   "English"),
+        ("zh",   "中文"),
+        ("th",   "ไทย"),
+        ("ar",   "العربية"),
+    };
+
+    /// <summary>
+    /// Initialise la langue à partir de la valeur enregistrée dans la config.
+    /// "auto" ou code inconnu → on prend la langue Windows si elle correspond
+    /// à une des langues supportées, sinon on tombe sur l'anglais.
+    /// </summary>
+    public static void Init(string? configValue)
+    {
+        var supported = new[] { "fr", "en", "zh", "th", "ar" };
+        var v = configValue?.Trim().ToLowerInvariant() ?? "auto";
+
+        if (v == "auto" || string.IsNullOrEmpty(v) || Array.IndexOf(supported, v) < 0)
+        {
+            // Auto-détection depuis la culture utilisateur Windows
+            var sys = CultureInfo.CurrentUICulture.TwoLetterISOLanguageName;
+            v = Array.IndexOf(supported, sys) >= 0 ? sys : "en";
+        }
+
+        _lang = v;
+        // On force aussi la culture système sur cette langue (formats date / nombre)
+        try
+        {
+            var ci = CultureInfo.GetCultureInfo(_lang);
+            CultureInfo.DefaultThreadCurrentCulture = ci;
+            CultureInfo.DefaultThreadCurrentUICulture = ci;
+            Thread.CurrentThread.CurrentCulture = ci;
+            Thread.CurrentThread.CurrentUICulture = ci;
+        }
+        catch { /* culture inconnue, on garde le défaut */ }
+    }
+
+    private static string T(string fr, string en, string zh, string th, string ar) => _lang switch
+    {
+        "en" => en,
+        "zh" => zh,
+        "th" => th,
+        "ar" => ar,
+        _ => fr,
+    };
+
+    // ==================== TOP BAR ====================
+    public static string TopBarCheckUpdates => T("🔄  Vérifier les MAJ", "🔄  Check for updates", "🔄  检查更新", "🔄  ตรวจสอบการอัปเดต", "🔄  التحقق من التحديثات");
+    public static string TopBarSettings     => T("⚙  Paramètres",       "⚙  Settings",         "⚙  设置",        "⚙  ตั้งค่า",          "⚙  الإعدادات");
+
+    // ==================== BODY ====================
+    public static string BodyVersions       => T("Versions", "Versions", "版本", "เวอร์ชัน", "النسخ");
+    public static string BodyVersionsHint   => T(
+        "Lance, installe ou supprime une version. Les versions installées et celles disponibles sur le serveur cohabitent.",
+        "Launch, install or remove a version. Installed and available versions can coexist.",
+        "启动、安装或删除版本。已安装的版本与服务器上可用的版本可以共存。",
+        "เปิด ติดตั้ง หรือลบเวอร์ชัน เวอร์ชันที่ติดตั้งและที่มีในเซิร์ฟเวอร์อยู่ร่วมกันได้",
+        "تشغيل أو تثبيت أو إزالة نسخة. النسخ المثبتة والمتاحة على الخادم يمكن أن تتعايش."
+    );
+
+    public static string FeaturedCurrent    => T("VERSION COURANTE", "CURRENT VERSION", "当前版本", "เวอร์ชันปัจจุบัน", "النسخة الحالية");
+    public static string SectionOther       => T("AUTRES VERSIONS",  "OTHER VERSIONS",  "其他版本",   "เวอร์ชันอื่นๆ",   "نسخ أخرى");
+    public static string ReleasedOn         => T("Sortie le ",       "Released ",       "发布于 ",   "เผยแพร่เมื่อ ",   "صدر في ");
+
+    // ==================== STATUS BADGES ====================
+    public static string StatusInstalled    => T("● Installée",          "● Installed",          "● 已安装",      "● ติดตั้งแล้ว",        "● مثبتة");
+    public static string StatusAvailable    => T("○ Disponible",         "○ Available",          "○ 可用",       "○ พร้อมใช้งาน",       "○ متاحة");
+    public static string StatusDownloading  => T("⬇ Téléchargement…",    "⬇ Downloading…",       "⬇ 下载中…",    "⬇ กำลังดาวน์โหลด…",  "⬇ جارٍ التنزيل…");
+    public static string StatusInstalling   => T("📦 Installation…",     "📦 Installing…",       "📦 安装中…",   "📦 กำลังติดตั้ง…",    "📦 جارٍ التثبيت…");
+    public static string StatusUninstalling => T("🗑 Suppression…",      "🗑 Uninstalling…",     "🗑 卸载中…",   "🗑 กำลังถอนการติดตั้ง…", "🗑 جارٍ الإزالة…");
+
+    // ==================== ACTIONS ====================
+    public static string ActionLaunch       => T("▶  Lancer",       "▶  Launch",       "▶  启动", "▶  เปิด",     "▶  تشغيل");
+    public static string ActionLaunchBig    => T("▶  LANCER",       "▶  LAUNCH",       "▶  启动", "▶  เปิด",     "▶  تشغيل");
+    public static string ActionInstall      => T("⬇  Installer",    "⬇  Install",      "⬇  安装", "⬇  ติดตั้ง",  "⬇  تثبيت");
+    public static string ActionInstallBig   => T("⬇  INSTALLER",    "⬇  INSTALL",      "⬇  安装", "⬇  ติดตั้ง",  "⬇  تثبيت");
+    public static string ActionCancel       => T("Annuler",         "Cancel",          "取消",   "ยกเลิก",     "إلغاء");
+    public static string ActionLater        => T("Plus tard",       "Later",           "稍后",   "ภายหลัง",    "لاحقاً");
+    public static string ActionSave         => T("Enregistrer",     "Save",            "保存",   "บันทึก",     "حفظ");
+    public static string ActionClose        => T("Fermer",          "Close",           "关闭",   "ปิด",        "إغلاق");
+    public static string ActionLicenseInsufficient => T("🔒  License insuffisante", "🔒  Insufficient license", "🔒  许可证不足", "🔒  ใบอนุญาตไม่เพียงพอ", "🔒  ترخيص غير كافٍ");
+
+    // ==================== MENU "..." ====================
+    public static string MenuReleaseNotes   => T("📜  Voir les release notes", "📜  View release notes", "📜  查看版本说明",      "📜  ดูบันทึกการเปลี่ยนแปลง", "📜  عرض ملاحظات الإصدار");
+    public static string MenuOpenFolder     => T("📁  Ouvrir le dossier",      "📁  Open folder",        "📁  打开文件夹",       "📁  เปิดโฟลเดอร์",         "📁  فتح المجلد");
+    public static string MenuUninstall      => T("🗑  Supprimer cette version…", "🗑  Uninstall this version…", "🗑  删除此版本…",     "🗑  ถอนการติดตั้งเวอร์ชันนี้…", "🗑  إزالة هذه النسخة…");
+
+    // ==================== LICENSE BADGE ====================
+    public static string LicenseNone        => T("Aucune license",    "No license",     "无许可证",       "ไม่มีใบอนุญาต",     "لا يوجد ترخيص");
+    public static string LicenseRevoked     => T("Révoquée",          "Revoked",        "已撤销",        "ถูกเพิกถอน",       "تم إلغاؤه");
+    public static string LicenseTooltip     => T("Voir / changer la license", "View / change license", "查看 / 更改许可证", "ดู / เปลี่ยนใบอนุญาต", "عرض / تغيير الترخيص");
+
+    // ==================== SETTINGS ====================
+    public static string SettingsTitle      => T("Paramètres", "Settings", "设置", "ตั้งค่า", "الإعدادات");
+    public static string SettingsLicense    => T("LICENSE",        "LICENSE",        "许可证",         "ใบอนุญาต",      "الترخيص");
+    public static string SettingsServer     => T("SERVEUR",        "SERVER",         "服务器",         "เซิร์ฟเวอร์",   "الخادم");
+    public static string SettingsInstallation => T("INSTALLATION", "INSTALLATION",   "安装",          "การติดตั้ง",     "التثبيت");
+    public static string SettingsCache      => T("CACHE DE TÉLÉCHARGEMENTS", "DOWNLOAD CACHE", "下载缓存", "แคชดาวน์โหลด", "ذاكرة التخزين المؤقت للتنزيلات");
+    public static string SettingsLogs       => T("LOGS & APPLICATION", "LOGS & APP",  "日志与应用",     "บันทึกและแอป", "السجلات والتطبيق");
+    public static string SettingsLanguage   => T("LANGUE",         "LANGUAGE",       "语言",          "ภาษา",          "اللغة");
+    public static string SettingsLanguageHint => T(
+        "Le launcher redémarrera pour appliquer le changement.",
+        "The launcher will restart to apply the change.",
+        "启动器将重启以应用更改。",
+        "Launcher จะรีสตาร์ทเพื่อใช้การเปลี่ยนแปลง",
+        "سيتم إعادة تشغيل المُشغِّل لتطبيق التغيير."
+    );
+    public static string SettingsTest       => T("Tester",     "Test",     "测试",  "ทดสอบ",   "اختبار");
+    public static string SettingsBrowse     => T("📁  Parcourir", "📁  Browse", "📁  浏览", "📁  เรียกดู", "📁  استعراض");
+    public static string SettingsClearCache => T("🗑  Vider",   "🗑  Clear", "🗑  清空", "🗑  ล้าง",  "🗑  مسح");
+
+    // ==================== ONBOARDING ====================
+    public static string OnboardingTitle    => T("Activation PROSERVE Launcher", "PROSERVE Launcher activation", "PROSERVE Launcher 激活", "เปิดใช้งาน PROSERVE Launcher", "تنشيط PROSERVE Launcher");
+    public static string OnboardingHeading  => T("Activer votre license", "Activate your license", "激活您的许可证", "เปิดใช้งานใบอนุญาตของคุณ", "تنشيط الترخيص الخاص بك");
+    public static string OnboardingBody     => T(
+        "Saisis la clé fournie par ASTERION. Elle te donne accès aux téléchargements jusqu'à la date de validité associée.",
+        "Enter the key provided by ASTERION. It grants you download access until the associated expiration date.",
+        "输入 ASTERION 提供的密钥。它授予您在关联的到期日期之前的下载权限。",
+        "ป้อนคีย์ที่ ASTERION ให้มา ซึ่งจะให้สิทธิ์ดาวน์โหลดจนถึงวันหมดอายุที่เกี่ยวข้อง",
+        "أدخل المفتاح المقدم من ASTERION. يمنحك صلاحية التنزيل حتى تاريخ انتهاء الصلاحية المرتبط."
+    );
+    public static string OnboardingLicenseKey => T("Clé de license", "License key", "许可证密钥", "คีย์ใบอนุญาต", "مفتاح الترخيص");
+    public static string OnboardingActivate   => T("Activer", "Activate", "激活", "เปิดใช้งาน", "تنشيط");
+
+    // ==================== UPDATE ====================
+    public static string UpdateAvailableTitle => T("Mise à jour disponible", "Update available", "有可用更新", "มีการอัปเดต", "تحديث متاح");
+    public static string UpdateDownload       => T("⬇  Télécharger", "⬇  Download", "⬇  下载", "⬇  ดาวน์โหลด", "⬇  تنزيل");
+}
diff --git a/src/PSLauncher.Models/LocalConfig.cs b/src/PSLauncher.Models/LocalConfig.cs
index 82204eb..2c17e10 100644
--- a/src/PSLauncher.Models/LocalConfig.cs
+++ b/src/PSLauncher.Models/LocalConfig.cs
@@ -6,6 +6,13 @@ public sealed class LocalConfig
     public string ServerBaseUrl { get; set; } = "https://example.com/PS_Launcher/api";
     public string InstallRoot { get; set; } = string.Empty;
     public string? LastLaunchedVersion { get; set; }
+
+    /// <summary>
+    /// Code de langue de l'UI : "auto" (suit la langue Windows), "fr", "en",
+    /// "zh", "th" ou "ar". Tout changement nécessite un redémarrage du launcher.
+    /// </summary>
+    public string Language { get; set; } = "auto";
+
     public LicenseConfig License { get; set; } = new();
 }