According to my experience, I think Google's translation into English is very good.
I sometimes use it when I don't find the words to write a sentence in English and it often suggests sentences in a very good English. It even manages to translate French idioms. I've also tested the translation from Chinese into English, which let me understand some Chinese I didn't got, even if it sometimes gives some non-sense.
However, be careful for other languages than English. The results can be very approximative. I once read translations from Chinese to French, which were very funny.