The most common translations are "à propos" or "environ" depending the sentence. Sometimes the translation can't really be done in that way because French verb aren't necessary followed by the same preposition. So if you give us more examples, we can give you more translations. "De quoi parles-tu?" or "De quoi es-tu entrain de parler ?" (about -> de) "Parce que je veux apprendre la culture parisienne" (about -> --- )

Merci Caroline! C'est tres utile!

Because it's a tricky answer, I wrote a whole article about it. http://www.italki.com/article/122/empty-words-and-cans-of-worms-translating-do-and-about-into-french#.U-XNgPldX3o

De quoi parlez-vous? Ou qu est ce que vous racontez? About ne peut pas etre traduit comme cela. Cela depend du contexte de la phrase.