feat(localization): expand language support and enhance UI for user settings

- Added support for additional UI locales including Cebuano and Spanish, improving accessibility for a broader user base.
- Updated language selection components in the AppHeader and SettingsWidget to reflect new language options, enhancing user experience.
- Enhanced localization of various UI elements across components, ensuring consistent language representation and improved user engagement.
- Implemented logic to synchronize user language preferences with backend settings, providing a seamless experience when changing languages.

frontend/src/views/social/VocabCourseListView.vue

@@ -2,9 +2,9 @@
   <div class="vocab-course-list">
     <section class="vocab-courses-hero surface-card">
       <div>
-        <span class="vocab-courses-kicker">Kurse</span>
+        <span class="vocab-courses-kicker">{{ $t('socialnetwork.vocab.courses.courseListKicker') }}</span>
         <h2>{{ $t('socialnetwork.vocab.courses.title') }}</h2>
-        <p>Öffentliche und eigene Lernkurse filtern, finden und direkt weiterlernen.</p>
+        <p>{{ $t('socialnetwork.vocab.courses.courseListIntro') }}</p>
       </div>
     </section>
 
@@ -88,7 +88,7 @@
         <form @submit.prevent="findCourseByCode">
           <div class="form-group">
             <label>{{ $t('socialnetwork.vocab.courses.shareCode') }}</label>
-            <input v-model="shareCode" placeholder="z.B. abc123def456" required />
+            <input v-model="shareCode" :placeholder="$t('socialnetwork.vocab.courses.courseShareCodePlaceholder')" required />
           </div>
           <div class="form-actions">
             <button type="submit">{{ $t('general.search') }}</button>
@@ -329,7 +329,7 @@ export default {
         await this.loadAllCourses();
       } catch (e) {
         console.error('Fehler beim Erstellen des Kurses:', e);
-        showApiError(this, e, 'Fehler beim Erstellen des Kurses');
+        showApiError(this, e, this.$t('socialnetwork.vocab.courses.createCourseError'));
       }
     },
     async enroll(courseId) {
@@ -339,7 +339,7 @@ export default {
         this.openCourse(courseId);
       } catch (e) {
         console.error('Fehler beim Einschreiben:', e);
-        showApiError(this, e, 'Fehler beim Einschreiben');
+        showApiError(this, e, this.$t('socialnetwork.vocab.courses.enrollCourseError'));
       }
     },
     openCourse(courseId) {