May I offer an alternative?
Since you have already gone into a lot of work making this and have also wisely chosen to use GitHub as a means of maintaining it, why not ask @Gazebo to be added as collaborators to the official repo and simply create new branches from the 'master'?
Each branch could be dedicated to a separate language and when you are suffuciently happy with the status you could push a merge of those files to the master.
You could also do this without being collaborators but I'm a bit rusty on pushing commits from separate forked repo to the original.
Just an idea.
Of course, we could just fork the orignial repo und send pull requests with the folders for different languages.
In theory, it should be no problem to add this folder structure to the main repo.
The only problem I see: At the moment the translating stuff happnes post-release. So everytime a new version gets released, the Makefile should not include all other languages, because the translation is not finished.
So how should the new languages be delivered? This solution here works fine, but you have to move the folders yourself.
It would be convenient to have the other languages in the main download file. Maybe everytime a new language is finished for a version, add it to the Makefile for building?