The issue appears to be in the MediaWiki:Common.js page, the issue doesn't happen in with safemode=1, specifically line 276 in Common.js seems to be the offending line causing the malformed redirects

The MediaWiki:Common.js snippet causing this seems obsolete to me (it seems to come from dewiktionary which does not use it anymore, we haven't used Squid for user traffic in years and afaik don't collect search analytics from ats/varnish logs). Since there are no local int-admins or sysops I'm tempted to simply remove that code. Thoughts?

Looking at https://af.wikibooks.org/w/index.php?title=MediaWiki:Common.js&action=history (folks likely not active on afwikibooks who made required edits in the past due to technical changes), I'd appreciate removing that code, yes.

In T299282#7624034, @Majavah wrote:

The MediaWiki:Common.js snippet causing this seems obsolete to me (it seems to come from dewiktionary which does not use it anymore, we haven't used Squid for user traffic in years and afaik don't collect search analytics from ats/varnish logs). Since there are no local int-admins or sysops I'm tempted to simply remove that code. Thoughts?

+1 that seems totally dead code.