The javascript that was triggering this broke because var span = document.getElementById('redirected_from'); doesn't find anything on the page, otherwise,

https://frp.wikipedia.org/wiki/Vouiquip%C3%A8dia:Redir%C3%A8ccion_vers_Vouiquil%C3%A9vros?debug=true#<t0>.23<t1>.23<img%20src=food%20onerror="alert(1)"/>

and

https://oc.wikipedia.org/wiki/Wikip%C3%A8dia:Redirect_cap_a_Wikilibres'?debug=true#<t0>.23<t1>.23<img%20src=food%20onerror="alert(1)"/>

and

https://wo.wikipedia.org/wiki/Wikip%C3%A9dia:Redirect_vers_Wikibooks?debug=true#<t0>.23<t1>.23<img%20src=food%20onerror="alert(1)"/>

would trigger.

Needs to get fixed, but not active so we'll get to it someday.

The code is no longer present on any wikis.

frp.wikipedia.org already didn't have it (was removed by a local admin in June last year).
orc.wikipedia.org and wo.wikipedia.org still had it, I removed it just now (diff 1, diff 2).

I also verified through mwgrep that code like it hasn't been introduced on any of the other 895 wikis, either ("redirected_from", "redirectedFromArticleDatas", etc.)

There is doRedirect() on https://or.wiktionary.org/wiki/MediaWiki:Common.js which passes var wiktDYMfrom = decodeURIComponent(location.href.replace(/^(.+[&\?]rdfrom=([^&]+).*|.*)?$/,"$2")); to mw.util.getUrl. Could be removed since T5339 is fixed, maybe.