Kotosov In my case, I would like him to have the ability to approve translated strings, so he could back me up if I won't be able to work on the project.
You don't really need mark translations as approved - unapproved translations are also exported to language pack and can be used right away by installing dev-master version (or when maintainer releases new version). Technically language pack can function without maintainer and with community contributions only. The main responsibility of maintainer is to review contributions to keep them consistent, and it is actually harder to do this if you have multiple people responsible for this.
If you still insist, I'll grant him maintainer permissions. But I feel that this request comes from misconception that you need to be maintainer to translate (he doesn't have any translations so far: https://weblate.rob006.net/user/LateNever/).
luceos What would be difference between co-maintainer and maintainer in terms of permissions?
Personally I think that it would be more efficient to react ad hoc on maintainer inactivity (we just did that for Turkish language pack), instead of adding "backup maintainer" that may loose interest in project before he will be needed. We already have some language packs with multiple maintainers, and most of them looks like maintained by single active maintainer anyway.
