@sstefan I guess you are referring to https://github.com/RocketChat/Rocket.Chat/tree/develop/packages/rocketchat-i18n/i18n ? Is an entire file missing or does a file need to be updated?
Ideally, if you can just contribute your changes upstream, then we can pull it down from there in the next release. Please see https://rocket.chat/docs/contributing/translating/ . Alternately, I can tell you how to build rocket.chat package from Cloudron source package until your changes are merged (it's very easy).