Implement personal section in navigation: Add a new 'personal' menu item with sub-items for language learning and calendar. Update localization files for English and German to include translations for the new section. Integrate personal routes into the router configuration for navigation.

frontend/src/i18n/locales/en/personal.json

@@ -0,0 +1,8 @@
+{
+    "personal": {
+        "calendar": {
+            "title": "Calendar",
+            "comingSoon": "The calendar will be available soon. Here you will be able to manage your appointments and events."
+        }
+    }
+}