To make a suggestion like this in French, one way is to use the "imparfait": "Et si on allait au cinéma dimanche?" or the conditional: "On pourrait aller au cinéma!" But you know, you're looking for the translation of an idiomatic expression, . You could google the type of sentence (the "function") you're looking for: "comment faire une suggestion en français", and you would find these: http://www.anglaisfacile.com/exercices/exercice-anglais-2/exercice-anglais-28230.php

How about = et si... ? What about = que penses-tu de... ? I think so = je pense que oui / je crois que oui I don't think so = je ne pense pas (que...)

I think so = je crois que oui I don't think so = je crois que non what about = qu'en est-il

how about hanging out with me ? what about Sunday?