I was thinking of a proposal for designing programming languages, but I am not sure whether it is a duplicate of an already existing proposal/beta site/SE site or if it is off-topic for a Q&A website.
I can easily (I think) get an audience for this so that wouldn't be a problem.
Area 51 is currently accepting proposals for subjects not already covered by our existing communities. This subject has been proposed a few times, but programming language design is on topic for our Computer Science site. It would be closed as a duplicate.
Depending on the nature of the questions that would be asked, your proposed site is probably a duplicate of one or more of
