(If you speak another language fluently, by all means say so. This is an asset. However, if you took Spanish or French in school but cannot remember more than two or three phrases, simply mention that you understand the language better than you speak it. Try this answer:)
I studied ____________________ (Spanish/French/German) in ___________________ (high school/college) and enjoyed it. I'd like to get some language tapes and increase my fluency.