+0

"Which other foreign language did you study?"

"Which other foreign languages have you studied?"

+2
Best Englishdid you study?

... referring to a period of time which has already ended, for example, while the listener was at a certain university (and is no longer there), or for example, from 2000 to 2015.

Best Englishhave you studied?"

... referring to a period of time that includes the listener's entire life up to the very moment you ask the question.

CJ

+1

In #1, you know he studied one other foreign language.

In #2, you know he studied at least one foreign language and possibly more.