Within Asia, Japanese is absolutely the most useful language, especially if you want to work at any good Japanese companies. Within Europe, it would be of great help to learn French & German, & actually, the number of native German speakers is even more than that of native French speakers. It's not an exaggeration. Within Latin America, it is of great importance & necessity to learn Spanish, along with Portuguese, but if you don't plan to go there for further study, for settling down, or for professional training, I think, Spanish wouldn't be the best choice for you, because there's hardly any good job opportunities related to Spanish or Portuguese, maybe you couldn't benefit so much from either of them, unless you were an excellent tour guide. Also, it depends on which language you like most, or what you want to do with this language.

如果你很熟练英语，你可以学法语，俄语。。。。。。

For you in college, I suggest Spanish. English is the official language of the European Union, so why learn their languages? Spanish is #3 in the world after English & Mandarin. It's also much easier than English and almost all other western languages. Maybe Korean or Japanese is more useful and easy for you though.

Italian, because I'd like to spend some time there.

Incidentally, by and large, Germans can speak good English, & they would like to talk to foreigners in English, particularly to those who are unable to speak German fluently & correctly. While Frenchmen have always insisted on speaking their own language --- French, no matter whether the foreigners could understand them or not. So, I think, perhaps French would be a little more useful, if you hadn't got a clear plan to take root in German-speaking countries. When all is said and done, German was, is, & still will be one of the most important & useful languages all over the world. Good luck!