The most important feature is, that the default works for every app and user without tedious setup, like now “english” is the default, it should be possible to change it it “german is the default”. IMHO in most installations all users will use the same single language in all applications.
“Force language” could be an option, but there is no real need to prevent someone to use a different language. If implemented it should be an only an option.
It is not just for two applications but all application to now and to come, where it is possible to change the default language.
How to open a feature? Here or on github?