Template categories

I do think that Category:Reference templates by language (where all the subcategories are) should be a part of Category:Reference templates (which has the interwiki links). Can you please explain why you reverted my categorization?

Because it's about to be deleted.

In that case, the interwiki links should move to the surviving category, right? And interwiki links for categories on Wiktionary are still maintained in the wikitext, not through Wikidata, right?

Yes and yes.