Related: http://labs.theguardian.com/digital-language-divide/
Is it possible to auto translate posts in most of other languages (at least Chinese, as it seems to have most of the users using internet after English), and to show them as auto translated and as original post? Would it be possible for multilanguage speakers to translate/edit them to others too?
I will come back later on Thursday; I have exams now. 
Possible? Yes. Useful? Probably not. Q&A relies on precise details and often specialized vocabulary that automated translation is going to royally mangle. Giving askers the impression that they can simply write a question in Spanish, Chinese, or whatever and magically have monolingual English speakers give them a workable answer in Spanish, Chinese, or whatever is a recipe for tears and lots of deleted posts. It is sometimes possible for someone who knows a little English to use a translation service to handle the bulk of a post, then fix it up, partly with the help of commenters. But the responsibility for being accurately understood in English lies with the poster; translation just isn’t good enough for us to take that over.
We can design our interface to be multilingual (although this is not part of the MVP). I agree with tuggyne however - auto-translating answers is no good thing to do. If users want auto-translate, they can just use browsers or plugins which offer it.
Even more, these auto-translate plugins are often what people who have difficulties with English are already using.