I’m not completely sure but I suppose you could as long as firebase would permit it. Could be wrong though, never used firebase.
Choosing country could either be through your own select option in angular or you could check what the phone’s default language is with a cordova plugin.
A q&a app like you’re suggesting is possible, though how far and how much real-time you want to use in it is really up to you and will really determine how much work you’ll need to put into it. From what I’ve read and seen from other users, firebase should also give you some good real-time functionality so your app should be capable of taking advantage of that benefit.