This is an English-only site, because it's far more likely that people will get support from other English-speakers. Poor English is better than no English, and we can usually salvage a good post out of even Google Translate if need be.
Otherwise, users run the risk of getting their question closed as "unclear" if someone capable of translating doesn't see it (which happens pretty often).
See badp's answer:
When the asker speaks Danish and the guy who could write the best answer to that question speaks Turk, everybody loses. Having everybody use English instead, even if it's poor English, is far better.
See, if a Q&A site can't get you answers for your questions it has failed. To do so, the Q&A site must connect the asker to as many potential answerers as possible. If there are not enough of those, not enough questions get answered and users won't come back.
Also, as Jacob pointed out, "We want to help people, but we are not a help desk." If you want help here, you need to put forward at least minimal effort to creating a question that we can understand and help with. We're not in a role of some desk-jockey who is paid to resolve your ticket no matter what. If we can't help you, we're going to move on to someone we can help. Terdon in this case:
We expect users to put the minimal amount of effort into their questions. That's one of the main reasons for downvoting and is what makes Stack Exchange so much better than the noise-filled forums that abound everywhere else on the internet. A user who simply posts their question in another language on an English-language site and can't even be bothered to i) attempt to write in English or, if they speak no English at all, ii) pass their question through Google Translate is failing to put any effort at all into the question.