This is why claiming to be a “prophet” (by any of a multitude of definitions) is so popular for cult leaders.
You can say you have information from a deity, one way or another, or even that you get special treatment from a deity. No special powers needed. If people believe in the deity and they believe you were chosen by that deity, to counteract that would mean counteracting the belief in the deity itself.
By the numbers: French or Arabic, as other commenters have mentioned.
But it really, really depends on where in the world you want to travel. If you’re interested in Asia, for example, neither French nor Spanish nor Arabic will help you much (save for some remaining French usage in Vietnam).
A better answer is: figure out where you want to go, then do the math on what to learn.