Hi, I'm good in English, Italian and Spanish literature.
So, Which type of Literature is on-topic in this site? Just English or Literature in other language too?
This would probably be a question for the Literature meta site if/when that's created. I don't know whether any of these Area 51 Discussion questions will get migrated to the meta site (and suspect not), so any consensus reached here may only be indicative of site policy rather than actually setting it.
That being said ... in my opinion,
literature in all languages should be on-topic.
I don't mean that the site should become one of those like, say, French Language or German Language which (as far as I know) accepts questions and answers which are not written in English. The language of almost all Stack Exchange sites is English, and this will surely be the case with Literature too. But questions written in English about works which were not written in English should certainly be on-topic. In fact, some of these have already appeared among the highest-voted example questions:
Yes, questions about literature written in a language other than English should be on-topic. In fact, users should feel free to quote literature in the original language it was written, and they should feel free to discuss any interesting puns/grammatical features/etc. that occur in the original non-English text. The one restriction should be that when users aren't quoting from literature their answers should be in English; this will be an English speaking site, even if we are discussing works not originally written in English.
As I understand it, this is the policy of most Stack Exchange sites that discuss texts written in languages other than English, such as the Mythology Stack Exchange, and the various religious Stack Exchanges that deal with non-English religious texts. Personally, as a contributor to the Mythology Stack Exchange, some of the answers I enjoy the most are the answers that quote mythology in the language it was originally written.
Of course, we can revisit this when we reach the private beta stage, but I think this policy makes the most sense, especially since it's what most sites in similar situations are already doing.
Yes; as long as the actual question is written in English.
The only "issue" would be whether you'd have enough expertise to have a good chance of receiving good answers. However, that's only as much of an issue as an obscure piece of work.
Stack Exchange is a community, one which is open to, and represents the entire world. As such you'd be surprised to see how many people could field those questions simply by the fact that they're humans from different parts of the world.