Why I would choose Japan and Japanese language:
1. I think Japanese tolerate foreigners more than Chinese.
2. Chinese language is more difficult to learn.
3. Chinese would preffer to have a Chinese person who will have learned your language and taken your job for a lower slary.
4. Japanese would probably pay you more.
5. Japan invests more money in international trades and projects than China.

The decision is all yours and you should think of it carefully what you really want for YOURSELF. Good luck!