diff --git a/app/Http/Controllers/SettingsController.php b/app/Http/Controllers/SettingsController.php
index 22d29a2..c81c0f6 100644
--- a/app/Http/Controllers/SettingsController.php
+++ b/app/Http/Controllers/SettingsController.php
@@ -9,6 +9,7 @@
 use App\Models\Setting;
 use Illuminate\Http\JsonResponse;
 use Illuminate\Http\Request;
+use Illuminate\Validation\Rule;
 use Inertia\Inertia;
 use Inertia\Response;
 
@@ -19,6 +20,7 @@ class SettingsController extends Controller
         'agenda_end_title',
         'agenda_announcement_position',
         'agenda_sermon_matching',
+        'default_translation_language',
     ];
 
     public function index(): Response
@@ -48,10 +50,16 @@ public function index(): Response
     public function update(Request $request): JsonResponse
     {
         $validated = $request->validate([
-            'key' => ['required', 'string', 'in:'.implode(',', self::AGENDA_KEYS)],
+            'key' => ['required', 'string', Rule::in(self::AGENDA_KEYS)],
             'value' => ['nullable', 'string', 'max:500'],
         ]);
 
+        if ($validated['key'] === 'default_translation_language') {
+            validator($validated, [
+                'value' => ['nullable', Rule::in(['DE', 'EN', 'FR', 'ES', 'NL', 'IT'])],
+            ])->validate();
+        }
+
         Setting::set($validated['key'], $validated['value']);
 
         return response()->json(['success' => true]);
diff --git a/database/seeders/CcliSettingsSeeder.php b/database/seeders/CcliSettingsSeeder.php
new file mode 100644
index 0000000..28354b5
--- /dev/null
+++ b/database/seeders/CcliSettingsSeeder.php
@@ -0,0 +1,17 @@
+<?php
+
+namespace Database\Seeders;
+
+use App\Models\Setting;
+use Illuminate\Database\Seeder;
+
+class CcliSettingsSeeder extends Seeder
+{
+    public function run(): void
+    {
+        Setting::firstOrCreate(
+            ['key' => 'default_translation_language'],
+            ['value' => 'DE'],
+        );
+    }
+}
diff --git a/database/seeders/DatabaseSeeder.php b/database/seeders/DatabaseSeeder.php
index 6b901f8..db42742 100644
--- a/database/seeders/DatabaseSeeder.php
+++ b/database/seeders/DatabaseSeeder.php
@@ -21,5 +21,7 @@ public function run(): void
             'name' => 'Test User',
             'email' => 'test@example.com',
         ]);
+
+        $this->call(CcliSettingsSeeder::class);
     }
 }
diff --git a/tests/Feature/SettingsDefaultLanguageTest.php b/tests/Feature/SettingsDefaultLanguageTest.php
new file mode 100644
index 0000000..7150bc6
--- /dev/null
+++ b/tests/Feature/SettingsDefaultLanguageTest.php
@@ -0,0 +1,87 @@
+<?php
+
+namespace Tests\Feature;
+
+use App\Models\Setting;
+use App\Models\User;
+use Database\Seeders\CcliSettingsSeeder;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use PHPUnit\Framework\Attributes\DataProvider;
+use Tests\TestCase;
+
+/**
+ * @mixin \Illuminate\Foundation\Testing\Concerns\InteractsWithAuthentication
+ * @mixin \Illuminate\Foundation\Testing\Concerns\InteractsWithDatabase
+ */
+final class SettingsDefaultLanguageTest extends TestCase
+{
+    use RefreshDatabase;
+
+    public function test_default_translation_language_is_seeded_with_de(): void
+    {
+        $this->seed(CcliSettingsSeeder::class);
+
+        $setting = Setting::where('key', 'default_translation_language')->first();
+
+        $this->assertNotNull($setting);
+        $this->assertSame('DE', $setting?->value);
+    }
+
+    #[DataProvider('validLanguages')]
+    public function test_accepts_valid_default_translation_language_via_patch(string $language): void
+    {
+        $user = User::factory()->create();
+
+        $response = $this->actingAs($user)->patchJson(route('settings.update'), [
+            'key' => 'default_translation_language',
+            'value' => $language,
+        ]);
+
+        $response->assertOk()->assertJson(['success' => true]);
+
+        $this->assertSame($language, Setting::get('default_translation_language'));
+    }
+
+    public static function validLanguages(): array
+    {
+        return [
+            ['DE'],
+            ['EN'],
+            ['FR'],
+            ['ES'],
+            ['NL'],
+            ['IT'],
+        ];
+    }
+
+    public function test_rejects_invalid_default_translation_language_via_patch(): void
+    {
+        $user = User::factory()->create();
+
+        $response = $this->actingAs($user)->patchJson(route('settings.update'), [
+            'key' => 'default_translation_language',
+            'value' => 'ZZ',
+        ]);
+
+        $response->assertUnprocessable();
+        $response->assertJsonValidationErrors('value');
+    }
+
+    public function test_exposes_default_translation_language_in_settings_props(): void
+    {
+        $user = User::factory()->create();
+
+        $this->seed(CcliSettingsSeeder::class);
+
+        $response = $this->actingAs($user)
+            ->withoutVite()
+            ->get(route('settings.index'));
+
+        $response->assertInertia(
+            fn ($page) => $page
+                ->component('Settings')
+                ->has('settings.default_translation_language')
+                ->where('settings.default_translation_language', 'DE')
+        );
+    }
+}