Hi!
In RDF exports of Wikidata[1] and in Wikidata Query Service, sitelinks were always encoded by url-encoding the sitelink text - i.e. link to "Category:Stuffed animals" were encoded as /wiki/Category%3AStuffed%20animals.
While this encoding produces a working link, after some time we've arrived to a conclusion that such encoding is very inconvenient, due to mismatch with how titles are encoded in Mediawiki, and this mismatch makes it harder to look up the links. See more in https://phabricator.wikimedia.org/T131960
We have decided to change the encoding, so that the encoding of the sitelink above would be /wiki/Category:Stuffed_animals. The encoding now should match how titles are encoded in Mediawiki codebase (non-ASCII characters that Mediawiki encodes will still be encoded as before).
Implementation of this change will require database reload, and during that time there might be inconsistent results returned for some time (some entities may have new sitelink encoding and some the old one). I apologize in advance for any inconvenience caused by that. I will announce additionally when the switch is process has started and when it is complete.
Thanks, [1] https://www.mediawiki.org/wiki/Wikibase/Indexing/RDF_Dump_Format