It’s awesome you’d like to help with BuddyPress translation! Happy to help you get started with translating on http://translate.wordpress.org. I’m Petya on wp Slack.
BuddyPress could use a Project Translation Editor for Chinese as well, so if you’d like to become one, you can post a request on https://make.wordpress.org/polyglots and we’ll put you in touch with the Chinese General Translation Editors so they can add you as a project maintainer.