German is pretty useless, unless you live either in Germany or near Germany, which I do, you might consider German. French is a beautiful language, but almost as useless as German, though it's more common than German. Spanish is a world language, spoken all over the world, so if you plan on travelling a lot in the future go with Spanish. Chinese is gamble, it might be very useful in the future. Latin however is not useless at all for several reasons; you'll learn the basics of the romance languages, so would definitely useful for learning Spanish or French in the future and of course in science, especially biology, Latin is an often used language, its grammar is not easy though.
Anyway, I don't speak Chinese, nor I speak Spanish very well, so I can't really comment on these. But Latin has been the most useful language for me. Of course I do have one of the best teachers I have to say (well, as I'm almost a fluent speaker after only three years I think I'm allowed to conclude that).