Some guy had been doing Chinese translating for phabricator.
And the main part is done well.
The origin version https://github.com/wanthings/phabricator-zh_CN
My forked version https://github.com/aelam/phabricator-zh_CN
Is it possible to add it as a built-in part?
We don't have any current plans on shipping i18n inside Phabricator yet. When we do, it's because we'll support what we ship. For now I think what some German users are doing (sharing a Paste file here, P1792) is perfectly fine.