How to get Add local description source displayed? Not shown here on https://www.mediawiki.org/wiki/User:Holger_Plickert_(WMDE)
What's the window width? Which browser and zoom level?

It's covering the page title here for a moment before it's moved up again.

Browser size 1280 x 721
Screen size 1280 x 800 (Retina)

No zoom. Chrome 72

This is curious, if I open the browser console (et al), it all collapses down (eventually after the reflowing). Close it again, and items reappear, hiding the watchlist star

One messages for those tab seem to come from MW core, and the other from VE

	"create-local": "Add local description",
	"visualeditor-ca-createlocaldescriptionsource": "Add local description source",

Some Vector tab reflow edge case?

The label for editing the local page as wikitext is actually "Create source" (see the HTML code), and only gets changed to "Add local description source" by JS (probably VE initialization code). This changes the width of the tabs, but the check whether collapsing some tabs is necessary doesn't happen again.
Ideally, the same message would be used both on server and client side, or at least a re-check should be triggered (I actually run a $(window).trigger('resize') on most pages, which fixes this issue).