Note, I do not know practice in China, but they should be CERTIFIED translations. How this is done and what is required varies by country (some countries use notary stamp after). Main thing I believe is stamp/official letterhead or similar and letter saying something like "I certify this is a true translation of document X" date signature position etc.. In most countries there will be some typical process used, like certified translator, qualificaiton, etc.
Most of eg former soviet union / many ex-Warsaw pact typical process includes notary but don't know about China.