What is the problem?
I am struggling to get some of the changes made for https://phabricator.wikimedia.org/tag/mediawiki-page-diffs/ working on an RTL wiki.
For example, trying to select text from one side of the diff actually selects it from the other (the feature introduced in T285793).
I also notice that diff-right and diff-left attributes (from T285776) are not flipped in RTL.
I have tried setting the user's interface language and $wgLanguageCode to ar.
This is on my local bare-metal machine with wikidiff2 1.12.0 installed (compiled locally).
Wiki(s): local wiki MediaWiki 1.37.0-alpha (930841b) 15:14, 1 September 2021 with wikidiff 1.12.0.