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/falukant.json

@@ -461,7 +461,9 @@
                 "selectStockType": "Lagertyp auswählen",
                 "costPerUnit": "Kosten pro Einheit",
                 "buycost": "Kosten",
-                "sellincome": "Einnahmen"
+                "sellincome": "Einnahmen",
+                "buyPartialError": "Fehler beim Kaufen eines Teils der Lagerkapazität.",
+                "sellError": "Fehler beim Verkaufen der Lagerkapazität."
             },
             "vehicles": {
                 "cargo_cart": "Lastkarren",