It may be worth putting Mandarin and English at the top - but then you get in to all manner of cultural sensitivity issues. I think the safest way is to list everything in alphabetical order (which, I know, has its own set of issues - but it how Wikipedia does it.)
I could set a cookie - but that has two main issues.
2) If a user mis-clicks on Japanese when they meant Dutch - how do they get back to change their preference?
Thanks for pointing out about the Google Translate API. I think I'm right in saying that translate.google.com/m is still going to work after that date though?