I'm not sure if this was the intention from T5267, but https://secure.phabricator.com/source/translatewiki/browse/master/projects/;00108900457eda804c9c786dd76ff96620a05195 is a one-time file, and is not updated when an upgrade happens.
Would it be possible to provide a repository where the i18n files are regularly updated in JSON format so that volunteers from Wikimedia can start working on T5267?