This is also related to Extension:Diff (https://www.mediawiki.org/wiki/Extension:Diff), but I think it's being caused by Wikidata Repo.
In some diffs, Wikidata shows the diff in a different language no matter which language the user interface is set to. For example try this link (notice the intentional uselang=en):
https://www.wikidata.org/w/index.php?title=Q2511165&diff=74940737&oldid=74022613?uselang=en The change as well as the properties being changed are in German instead of English. Also, https://www.wikidata.org/w/index.php?title=Q375550&diff=72741582&oldid=72711136&uselang=en is in Finnish.