According to the documentation and especially the Language Switcher, we're supposed to be able to do :
But there is "maybe" an issue when you are in and Match/URI if you don't set something for the default siteaccess.
In this case I want the "/" without any URIElement to be the siteaccess "site"
But it doesn't work because the kernel doesn't find the matcher for the default siteaccess, I have the notice because we enter here :
I figured out a workaround :
I'm not sure, how to fix this case.
Probably here : https://github.com/ezsystems/ezpublish-kernel/blob/master/eZ/Bundle/EzPublishCoreBundle/DependencyInjection/EzPublishCoreExtension.php#L88
I'm not event sure if that is an issue, but it was completely possible in eZ 4, maybe a tip in the documentation could be enough.
Otherwise, I did a PR with another workaround. I'll put it in comment.