Thread:Talk:Mobile support in MediaWiki core/Here's what Google Webmaster Tools has to say/reply (13)

It looks like the default is already true.

That setting looks like a workaround to an indexing issue. One that theoretically could be fixed by adding a mobile rel=alternative the way Google describes.

((I reported this as T91183))

I'd recommend you leave that setting out of your config. That way if MobileFrontend fixes the issue things will just start working and get even better for your site, instead of your config overriding the improvement and downgrading your indexing.