Unfortunately, GrapheneOS doesn't have people available to translate into many different languages. I've read on here and in the Matrix rooms that they'd really like to support more languages, but they're not in the position to do that. So, everything is just in English, except the parts of Android that are already localized by Google.
As for typing, there've been others on here who've talked about keyboards and Asian language support. Some have found some open source keyboards to be kind of bad at Asian languages. I personally think Google's GBoard is okay at typing in Chinese. Not as good as iOS was, but better than any other keyboard on Android that I've tried. Maybe you can try GBoard?