Per T108630, HotCat is currently broken on many wikis that have local copies of the old gadget code (rather than importing the code from Commons). We should identify the wikis that have local copies, and fix them.
They can either be fixed by applying the same fix that was used on English Wikipedia and Commons or by switching them to import the Gadget code directly from Commons or English Wikipedia (Commons is probably better).
https://en.wikipedia.org/wiki/Wikipedia:HotCat - English Wikipedia documentation
https://commons.wikimedia.org/wiki/Help:Gadget-HotCat - Commons documentation