Sounds like you’ve rolled your own localization system for your game. Unreal does provide one that you can read about here:
If you want to use your own localization system you can still use Unreal’s internationalization system which provides the device/OS desired locale information for you.
FInternationalization::Get().GetCurrentCulture();
FInternationalization also has a OnCultureChanged() event that you can listen to if you allow your users to change their locale in-game.