It doesn't specify this anywhere on the Tour page and I cannot find a meta question that directly answers this question (if one exists, please direct me there). Are questions on SE (and *nix.SE in particular) expected to be in English? If so, is there a reason that "Not in English" is not a flag option?
See this meta post on the topic. Yes only English is allowed. If posts are in anything other than English they should be either translated by the OP or closed/deleted.
*excerpted the highest UV'd answer there -
The Stack Overflow Trilogy has an official policy on non-English questions:
It is not, nor has it ever been, our goal to be the one place in the world for all programming information in every possible human language.
Direct question posters to native language resources. It is not the community's goal to teach English. The question asker should put some effort into the question. As long as the question is in salvageable English and makes some modicum of sense, it should be edited and improved like any other post.