This breaking change is relevant for anyone who consumes Wikidata RDF data through Special:EntityData (rather than the dumps) without using the “dump” flavor.
When an Item references other entities (e.g. the statement P31:Q5), the non-dump (?flavor=dump) RDF output of that Item would include the labels and descriptions of the referenced entities (e.g. P31 and Q5) in all languages. That bloats the output drastically and causes performance issues. See Special:EntityData/Q1337.rdf as an example.
We will change this so that for referenced entities, only labels and descriptions in the request language (set e.g. via ?uselang=) and its fallback languages are included in the response. For the main entity being requested, labels, descriptions and aliases are still included in all languages available, of course.
If you don’t actually need this “stub” data of referenced entities at all, and are only interested in data about the main entity being requested, we encourage you to use the “dump” flavor instead (include flavor=dump in the URL parameters). In that case, this change will not affect you at all, since the dump flavor includes no stub data, regardless of language.
This change is currently available for testing at test.wikidata.org. It will be deployed on Wikidata on August 23rd. You are welcome to give us general feedback by leaving a comment in this ticket.
If you have any questions please do not hesitate to ask.