I'd like to throw a few thoughts on the matter, although for now I'm not sure whether we should accept or not.
Gestures are certainly an important part for communicating, as much as intonation or body movement. The intonation field is treated in Linguistics studies, for example.
Anyway, there are some gestures that are international, but some are peculiar to a given nation and some of them even only to certain regions. But even though all of these are important in helping the utterance having its desired effect on the interlocutor, they might get interpreted and that's the problem.
I think that most of them might generate discussions and debates. I'd add them to the "on-topic park" but first we have to consider that they're not a definite field, at least for some of them. And even grammar, that is kind of stricter and more definite, generates debates sometimes.
So, should we consider as on-topic questions like:
- What is the English gesture to convey [message]?
- In our country X we have this, what is the English equivalent?
- What's the difference in doing this gesture in U.S. or UK?