being an expert who is fully proficient in Portugus, Espaol, Italiano, Arabic, Russian, Svenska, Franais, Deutsch, Armenian, Danish, Basque, Galician, Tibetan, many regional native dialects of Madagascar, Nordic, Bengali, Classical Quich and Yucateco Mayan (and working on Creole) i would advise 'English' to be your best bet..
but if you already know that then Mandarin/Cantonese/Japanesian are good prospectively, and French is widely spoken thru-out Europa if you want to go down that route.
Its (French) is also a language closely related to its latin neighbours of Portuguese, Spanish, Italian and Romanian. So if you get fluent in French its not hard to pick up any of the above.
i think i will give one of the Asian tongues a go at Universidade.. since i am already quite acquainted with the latin-based lnguas.