If a question belongs to another site, and I am voting to close it, how can I choose the right one? When selecting "This question belongs on another site in the Stack Exchange network" I can only see UX.SE meta site.
It's not a bug since it's a moderator only option to migrate the question away to another site. Often we communicate with the receiving site mods to know if they want it, think it suits their site objective and is as well written as it's supposed to be.
Your job could be to suggest move to another site using the comment on close vote.