This is not a general problem on RTL wikis with LTR user interface language. It only occurs on arwiki. For example it does not occur on fawiki: https://fa.wikipedia.org/w/index.php?title=Foo&action=edit&uselang=en

arwiki tweaks some RTL/LTR settings in https://ar.wikipedia.org/wiki/ميدياويكي:Common.css and https://ar.wikipedia.org/wiki/ميدياويكي:Common.js:

Common.js:

/* Add class=mw-content-ltr to class=ltr and dir=ltr */
$(".ltr, div[dir*='ltr']").addClass("mw-content-ltr");

Common.css:

.mw-content-ltr {
text-align:left;
}
 
.mw-content-rtl {
text-align:right;
}

This cause this problems.

It would be possible to add a workaround in WikiEditor to prevent such problems. I think it would be better to fix or remove the tweaks in arwiki.

Pinging @Ladsgroup, maybe he knows why ar.wp does this, or someone else who might know.
It's outside the purview of phabricator really, but keeping it open for just a bit longer won't hurt..

I have no idea why users of Arabic Wikipedia did this. I can only guess, based on the source code, that they might wanted to keep LTR material (common.js pages and similar types of pages) LTR, not RTL. It was a bug that was solved a very long time ago and I remember Persian WP had a workaround for it but then we deleted it. If you can find a discussion even in Arabic. I might be more helpful. :)

Yeah, no luck there. I'm wondering if we should just ask a global interface rights person to intervene to remove those, and then leave their community a message referring to this ticket...

In T73661#2061017, @TheDJ wrote:

Yeah, no luck there. I'm wondering if we should just ask a global interface rights person to intervene to remove those, and then leave their community a message referring to this ticket...

I'd be happy to do so if needed.

I'll first drop a line to the last person to have made several edits to their Common.css file. https://ar.wikipedia.org/w/index.php?title=نقاش_المستخدم:زكريا&diff=18547297&oldid=18496554

arwiki tweaks have been removed. Thanks