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/personal/CalendarView.vue

@@ -2,9 +2,9 @@
     <div class="calendar-view">
         <section class="calendar-hero surface-card">
             <div>
-                <span class="calendar-kicker">Planung</span>
+                <span class="calendar-kicker">{{ $t('personal.calendar.kicker') }}</span>
                 <h2>{{ $t('personal.calendar.title') }}</h2>
-                <p>Termine, Geburtstage und eigene Einträge in einer strukturierten Übersicht.</p>
+                <p>{{ $t('personal.calendar.intro') }}</p>
             </div>
         </section>