https://www.mediawiki.org/wiki/MediaWiki_1.21/wmf6#Most_important_changes
This week and next week we're deploying a new version of MediaWiki to your wiki, as usual. This upgrade is now out to mediawiki.org and test2.wikipedia.org in case you want to try it out before it comes to your wiki -- for instance, you could log in and put your user scripts in your userspace to make sure everything still works. Key changes:
Display changes: * The message "wikimedia-editpage-tos-summary" (displayed below the edit form) has been removed; if it was customized on your wiki, its contents will have to be merged with "wikimedia-copyrightwarning". * We changed the wording of the protectedpagetext message to include moving and other actions. * MediaWiki:Contributions now reflects the gender of the user. * We're displaying IPv6 addresses more nicely.
Fixes: * Bogus page creation e-mail notifications were being sent when a page was actually being deleted. We think we've fixed that. * We fixed the mobile version of the website so that, if you disable images, it doesn't also strip other content. * Your "enhanced changelist" displays minor/bot changes better.
New: * There's a new DynamicSidebar - tell us if your sidebar acts weird. * TimedMediaHandler now supports embedding a smaller audio player of 35-pixel width, and reorders the controls so that small players get a play/pause button and volume first. * In WebFonts we've added the Gubbit font, replacing Kedage, for Kannada.
As always, more at https://www.mediawiki.org/wiki/MediaWiki_1.21/wmf6 and deployment dates at https://www.mediawiki.org/wiki/MediaWiki_1.21/Roadmap . Please let us know of any bugs! Thank you for your feedback!