The project already contains language %04X. No change is made.
Indicates that the new language that you have chosen is already present in the project. This leads to duplicate translations and is therefore prevented.
- Language identifier of the new language
If you want to change the language, choose one that isn't already present in the project. If you are juggling a number of languages around (for example, to start creating a new localization), then it might help to change them in a different order that prevents duplicate languages.