I've definitively had the case of having all the codebase in English (not our native language), since all concepts mapped easily, and then a new concept appears

I've definitively had the case of having all the codebase in English (not our native language), since all concepts mapped easily, and then a new concept appears and damned if I know how to translate it! So now we're stuck with a single non-English term in the codebase, which is a blot on the whole work :(