Seen in beta labs in Firefox (at least) http://en.wikipedia.beta.wmflabs.org
As a logged-in user
Click the cog icon on any page
Click the ellipsis button ("...")
Nothing happens. Clicking the ellipsis button should bring up a large "Display language" dialog. On enwiki the "Display language" dialog is visible, on beta labs clicking the ellipsis does nothing.
This would likely be the result of merged code from today https://gerrit.wikimedia.org/r/#/q/status:merged+project:mediawiki/extensions/UniversalLanguageSelector,n,z
Version: unspecified
Severity: major