itch.io

I think primarily English to Chinese, but I'm not 100% sure.

The best bet is likely to ask TW_Coffee_Ghost, but they do have an about page on their website here, which comes out really clearly in google translate: https://hazmole.github.io/Free-Open-TRPG-Translation/about/

From that page, it sounds like their priority is open source/creative commons games, translated from English to Chinese.

Also I don't know anything about the Chinese ttrpg scene, but if there's any ttrpgs that have been translated from Chinese to English I'd love to check them out.