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/components/TermineWidget.vue

@@ -1,10 +1,10 @@
 <template>
   <div class="termine-widget">
-    <h2>📅 Termine</h2>
-    <div v-if="loading" class="loading">Lade Termine...</div>
+    <h2>{{ $t('widgets.appointments.title') }}</h2>
+    <div v-if="loading" class="loading">{{ $t('widgets.appointments.loading') }}</div>
     <div v-else-if="error" class="error">{{ error }}</div>
     <div v-else-if="termine.length === 0" class="no-termine">
-      Keine bevorstehenden Termine
+      {{ $t('widgets.appointments.empty') }}
     </div>
     <div v-else class="termine-list">
       <div v-for="termin in termine" :key="termin.datum + termin.titel" class="termin-item">
@@ -50,7 +50,7 @@ export default {
         this.termine = response.data;
       } catch (error) {
         console.error('Error loading termine:', error);
-        this.error = 'Termine konnten nicht geladen werden';
+        this.error = this.$t('widgets.appointments.loadError');
       } finally {
         this.loading = false;
       }
@@ -64,7 +64,16 @@ export default {
         month: 'long', 
         day: 'numeric' 
       };
-      return date.toLocaleDateString('de-DE', options);
+      return date.toLocaleDateString(this.getDateLocale(), options);
+    },
+    getDateLocale() {
+      const locale = this.$i18n?.locale;
+      return {
+        de: 'de-DE',
+        en: 'en-GB',
+        es: 'es-ES',
+        ceb: 'fil-PH'
+      }[locale] || 'de-DE';
     }
   }
 };