hey there! you need to make sure that the language you are adding is a part of .net SystemLanguage enum and that the name matches the file name you have for localization

the error suggests that you are trying to use Afrikaans whereas the file for it is not present (or named differently)

https://github.com/Enigo/UnityAdvancedLocalization/blob/master/Assets/Scripts/LangResolver.cs#L25