ad 4) I was hoping we could decide on creating language packs instead of using releases to update and add languages.
This is straightforward from a users' perspective, IMO.
It seems that, in the end, this would be like comparing two lists of package-key.message-key 's
It would be important to be able to retain the existing translation, while updating your system, BTW.
I'm aware that it takes effort to prepare/update the system-list (depending on the packages and versions installed) and language-pack (depending on changes of the translation-server), but I would prefer this over new releases.