I wouldn't mind knowing how to speak Italian because I think it's one of the sexiest languages. I'd also like to know how to speak Japanese as I've always been the teensiest, tiniest, most subatomic bit obsessed with that country. I used to wanna live there. Now I just want to visit, but it'd still be nice to be able to interact with the locals.
Japanese. I already know Eng + Esp. I know a little bit of French, but I've always wanted to learn Japanese. After that, Chinese because we all know that China is pretty much going to rule the world soon. Might as well learn the language ahead of time.