For your multi-language app I'd recommend using https://angular-translate.github.io/ which allows you use multiple methods for translating as well as customizing what the translations should be under each language. The getting started section should explain it fairly well (I recommend looking into the translate filter).
Unfortunately I don't have anything for firebase and image saving is something I'm not solid on myself but on your question regarding a q&a app, can you clarify what exactly you mean by that or what you want it to do?