I tried to use the ?setlang= URL parameter in the Incubator to set a language. It worked on the desktop, for example using the URL https://incubator.wikimedia.org/wiki/Wp/kcg?setlang=kcg .

But it doesn't seem to work on mobile, with the URL https://incubator.m.wikimedia.org/wiki/Wp/kcg?setlang=kcg . Nothing happens, and I stay with the same language.

It's possible to go to the desktop mode, go to preferences, and select the language, but given the increasing number of mobile-only users, it would be nice to be able to do it without this workaround. In particular, I encountered people who use several languages that already have their MediaWiki localization working, but still don't have their own Wikipedia domain. For them, it would be useful to see the localization working in the Incubator, but to make it work, they apparently have to go through preferences in the desktop mode. It would be great to do it completely in the mobile web mode.

I'm not sure whether the problem is in ULS, MobileFrontend, or Core, so tagging all of them.