User blog comment:DaNASCAT/Technical Update: September 9, 2015/@comment-1065656-20150910111233/@comment-126761-20150910123049

MediaWiki:Chat.js and MediaWiki:Chat.css have actually been loading natively for several months. We don't support loading the /chat.js and /chat.css user subpages though - but that code can be placed in your global personal CSS/JS pages instead.