The brain builder is “Study English”–not “Don’t Study Foreign Languages”. English has an enormous body of substantive literature, including translations. (Is there a translation of Proust into Swahili?) English also has some of the world’s most excellent reference books, newspapers, magazines, films, documentaries, and other media. For the sake of your intelligence, don’t neglect the study of English. But that’s advice for native and near-native speakers. German speakers should study German; French speakers, French; etc.

People frustrated with learning a foreign language should quit. It’s not necessary for their intellectual development. (Most the great works of the Occiden–books and films–are translated into English.) Yes, studying languages builds your brain, but so does carpentry.

For the other people, here’s a litany of the most important languages of Western literature: Latin, Greek, Italian, French, German, Spanish and Russian. If you’re learning one of those languages, try patiently reading a classic (as by Virgil, Homer, Dante, Proust, Goethe, Cervantes and Tolstoy, respectively) in the original language, with a dictionary and grammar reference beside you. That’ll probably be the most profitable practice and use of an acquired language for your intellectual development.