The servers you pick in the launcher does not change your lobby server. It changes the servers you get matched to.
There is a ping-lock in the launcher that prevents players from China for example to match to EU servers. But that's easily circumventable with a VPN.
I am sure that the US, EU and UAE share the same lobby but I do not think that China does. Why? Because chinese names have not appeared before very recently. If China would have shared the same "GLOBAL" lobby then I should have seen chinese names now and then in the past too, right?
I believe that due to them using a VPN located outside of china they access the same lobby server that we use. If you can prove me wrong then I will gladly concede that I was wrong but so far it's all assumptions.