What you talk about are the young guys. But that is not the average WoW player.
I with my 25 years are only quarter of the Classic players. The Majority is 40-50 year old.
And as Malou described:
I have many of those 40-50 year old guys in my guild. So wandering on Hydraxian Waterlords would mean that we german guys take over an english Realm and so more or less force the natives to speak german despite them being the home. And if you go by the majority like you stated here:
then this is not true as there are more german roleplayers then english ones.
It whas said in the discussions about server closure that Celebras has more active players then all the other closed realms together.
So if they let open only one RP Realm it should be Celebras.
That does not mean I want to deny the guys from Hydraxian Waterlords or Zandalar Tribe their server as I am happy for them that they can at least RP like a character from that universe, in their own native language. While from my personal point of view I would agree with that just letting one permaflagged as PvP could be a substitute I still want them to keep their server as it seem for them to be important for the flair to be this way. Because I can only see in RP the problem with the language barrier and so keep them on one Realm would maybe be better, I hope they could still have their fun on their PvP Server as it does not interfere with my fun.
Anyway if we go by the numbers you love so much then the choice should have been Celebras.