This bug is blocking deployment of the tabbed languages gadget on the English Wiktionary (wikt:en:MediaWiki:Gadget-TabbedLanguages.js), which was approved by vote a few years ago: wikt:en:Wiktionary:Votes/2012-10/Enabling Tabbed Languages. It requires loading from the top for a number of reasons, such as conditional running of CSS based on cookies.
He's referring to T29488, of course.
Splitting this issue out to a separate bug report, as whatever issue this gadget is hitting is obviously divergent (if not tangential). Possibly related to T29488, possibly not, and possibly solved by a different solution.