@Volker_E Should we make the tabs wrap, or make them scroll? (for the record, the current design for tabs on Special:Preferences makes them wrap)

Note that while my screenshot is small, this is a real concern even for normal-sized screens – with all the extensions we have installed on Wikimedia wikis, Special:Preferences can have ten tabs, and in some translations (e.g. Polish and German) they get pretty unwieldy: https://commons.wikimedia.org/wiki/Special:Preferences?uselang=de. And OOUI's design uses a larger font and wider spacing than the current one.

@matmarex We should definitely avoid horizontal scrolling of tabs.
Wrapping sounds like the minimum compromise, although it's, especially with a large number of tabs, also not a good user experience, as users might for example loose context where they are.

A possible big step forward would be to transform it into a slide-out or dropdown menu on small screens, similar to this.

Change 379309 had a related patch set uploaded (by Bartosz Dziewoński; owner: Bartosz Dziewoński):
[oojs/ui@master] IndexLayout: Handle long lists of tabs

https://gerrit.wikimedia.org/r/379309

Do we have to support this? Button groups neither wrap nor scroll, you are just supposed to design your interface around that :)

Another option would be to set max-width to (100/n)%, or use a table row layout, then ellipsis any text that doesn't fit.

If we want to use the tabs on Special:Preferences in MediaWiki, per T117781: Convert Special:Preferences to OOUI, then we have to. With a few extensions installed there are definitely enough tabs to run out of space even on medium-sized screens (1200-1400px). Unless we want to change the interface to something different in that case (let's discuss on that task if so).

And what about the ellipsis approach? (which browsers use for multiple tabs...)

That becomes a big problem with many tabs, but is already problematic on a small number without any other hint. Browsers often provide a different approach to be able to see the full list of open tabs.
While the interface with the number of tabs is provided by “us”. How would you approach this on mobile (320px width) when all tabs get truncated and all tab titles partly replaced by ellipsis…?

I don't think that's likely here, if you have so many items that lots of scrolling is required you should probably be using BookletLayout instead. On mobile I don't think long tab lists are ever a good idea.

Change 379309 merged by jenkins-bot:
[oojs/ui@master] IndexLayout: Handle long lists of tabs

https://gerrit.wikimedia.org/r/379309

@Esanders That's why I've referred to different solutions of making tabs a dropdown menu when there's not enough available screen space. That is a better solution, more satisfying on both, desktop and mobile.