How familiar are you with regional variations on each language you speak?

Fluency in a language doesn't guarantee your ability to translate any text in that language, particularly when working with unfamiliar dialects and terminology. The interviewer is interested in how wide your reach might be. This question might also indicate that they need such a skillset on their team. Be prepared to be tested on this following your interview, so don't use this as an opportunity to over-fluff your abilities.