[trans platform] Divide reviewers in language groups
Very few contributors make changes on languages that are not their main translation language.
Following the principle of least privilege, we can create Review roles per language, so we can give reviewer status to more contributors.
This groups could also be used to send emails to reviewers of each language on #17650
Example: A new group wants to start translating a language we don't speak at all, and we have no reference about them. It will feel more comfortable to only give them review status on their language, while we try to find someone to check they are translating what the documentation says.