During the cleanup of the MediaWiki message groups on translatewiki.net, the need emerged to:
- rename "core" to something prefixed with "mediawiki"
- rename "core-0-mostused" to "mediawiki-top" https://gerrit.wikimedia.org/r/191095
- TWN is no longer MediaWiki-only,
- the ID is less important in TUX, while it used to determine ordering in the Special:Translate dropdown.
The issue is that we have thousands of lingering links translators follow from other wikis, and we don't want to break them. There should be a configuration variable to add an ID alias which redirects to a canonical ID, at least for Special:Translate. (Could be done in webserver redirects but that's ugly.)