How to find a way to help translating the site with multi-language?

The user interface for my site is multi-language supported. But some of words are just translated from Google. But they phrases are inaccurate.

I want to know if there are any online services or communities to help translate the site? I would prefer the translation be done by a person?

It is just some interface words within some PHP files. It`s too expensive to hire a professional translator to just translate those files.

Have you checked out Mechanical Turk? One of the examples they mention is "Human powered translation services" I have no idea how much it will cost. You might also need to have it translated 3 or 4 times to make sure you are getting an accurate translation.

Yet another option: ask your users!

Now of course this may only really apply if your site has a healthy audience, but I'm guessing many of your international users would be eager to correct a faulty Google translation if it only took a couple of clicks!

I worked for http://www.mygengo.com for a bit in 2010. They have a great API for getting translations, and an open took called string so you can collaborate with folks to get translations instead of paying for them. Mygengo then uses your collaboration as a means to auto translate things if people use the same words as you do.

We used to ask our users, but for some languages we have only a few, so their unavailability held us back. Last time I used vWorker to translate a few messages we have added to our installer to five different languages, then did a cross-check. Would engage most of the translators again.

Evernote uses something called Pootle and it looks very interesting. You should check it out, it might be what you are looking for.

Another possible resource could be cloud translators like Lingoking. There are human, professional translators and you can choose the area of expertise too. No idea about prices, but ask for a quick proposal.

I just saw the website not english everywhere, even if english language is choosen though. (Might be, because it is brandnew ;)

Have you thought of posting for international students willing to pick up freelance work? People advertising "certified translation" are not necessary for this kind of work. To keep costs down, provide of list of labels and messages in file and say, "here; fill in the blanks." If you point to a translator and make them go through your site, that'll be more work.