I had to translate my China police certificate, and my HR directed me to the local notary office. They notarized the copy of the original document as well as the translation of the original document. I don't even think they provided the translator's certificate, but I think I read on this forum somewhere that the translator's certificate is fine. However, if it's not too difficult for you to get the notarization, I think you might as well get it. Better safe than sorry, after all.