Probably if there are developers that speak/write/understand that language, By understanding I mean questions as well as explaining technical things within Hugo. And by developers I mean people deeply involved in Hugo’s code. If there is nobody that can answer questions it will be a self-help-group without solutions and not useful I think.
Maybe a post in “meta” like “Do we want a Greek language category” would be advisable per language and then some kind of counting of votes and user-types within a certain amount of time to see if it is even required.
New Stackexchange forum topics are created that way: https://area51.stackexchange.com/ - well, not completely that way, they have plenty of complicated rules, but there are phases where they evaluate if there is enough interest in a topic before creating that topic.