What is the fastest way to learn a foreign language?

The fastest way to learn a language is to read, write and think in the language as often as possible—you'll considerably increase the number of hours you spend interacting with the language each week.

Which foreign language should I learn first?

All in all, Mandarin is the best language to learn because of its growing economy and number of language speakers. Spanish and Arabic are next for the the top spots for the best language to learn abroad because of the sheer demand and job opportunities for them.