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/i18n/locales/de/general.json

@@ -41,6 +41,59 @@
     "message": {
         "close": "Schließen"
     },
+    "appShell": {
+        "header": {
+            "tagline": "Community-Plattform",
+            "beta": "Beta",
+            "backend": "Backend",
+            "daemon": "Daemon",
+            "language": "Sprache"
+        },
+        "footer": {
+            "systemLabel": "System",
+            "noOpenDialogs": "Keine offenen Dialoge",
+            "activeWindows": "{count} Fenster aktiv",
+            "systemReady": "System bereit",
+            "systemStatusUnavailable": "Der Systemstatus ist in dieser Ansicht derzeit nicht direkt verfügbar."
+        }
+    },
+    "widgets": {
+        "dashboard": {
+            "dragHandle": "Verschieben",
+            "loading": "Laden..."
+        },
+        "birthdays": {
+            "today": "Heute!",
+            "tomorrow": "Morgen",
+            "turningAge": "(wird {age})",
+            "inDays": "{count} Tage",
+            "empty": "Keine Geburtstage von Freunden sichtbar"
+        },
+        "upcoming": {
+            "today": "Heute",
+            "tomorrow": "Morgen",
+            "timeAt": "{time} Uhr",
+            "allDay": "Ganztägig",
+            "empty": "Keine anstehenden Termine"
+        },
+        "appointments": {
+            "title": "📅 Termine",
+            "loading": "Lade Termine...",
+            "empty": "Keine bevorstehenden Termine",
+            "loadError": "Termine konnten nicht geladen werden"
+        },
+        "list": {
+            "noEntries": "Keine Einträge",
+            "entriesCount": "({count} Einträge)",
+            "fieldsCount": "({count} Felder)"
+        },
+        "news": {
+            "emptyValue": "—"
+        },
+        "falukant": {
+            "emptyValue": "—"
+        }
+    },
     "gender": {
         "male": "Männlich",
         "female": "Weiblich",