For those who are unaware of this feature, it basicly means that for example a group of Alliance consisting of French servers may be pitted against a group of Horde players from Spanish servers. A common misconception is that players from these servers with an other language will be mixed with the English servers, which is not the case.
Anyway, the goal of course is to decrease queues. There may not be enough English-speaking Alliance out there for you to smash, but perhaps there's a whole bunch of French Alliance queueing. So yeah, nice find.
Except not all battlegroups are being merged.
Battlegroups that will not be merged
English – Blackout, Misery and Vindication
German - Blutdurst
Russian - Шквал (Flurry) and Вихрь (Whirlwind)
In a suprising twist, six battlegroups are not being merged, for unknown reasons.
Blackout, Misery and Blutdurst are all big battlegroups. Vindication and the two Russian ones aren't.
Now, being from Vindication myself, I was quite suprised with this. The view I have of the battlegroup is a fairly low activity battlegroup, with an overrepresentation of Horde. I have instant queues, but I bet the Horde doesn't - from what I hear they can vary between 30 mins - an hour and a half.
A possible explanation for not merging the Russian battlegroups could be due to cyrillic characters posing a problem. Perhaps they don't want English/French/German/Spanish players to have to try and pronounce a Russian player's name over Vent, or something. Still sounds like a bit of a dumb excuse.
Others are bringing up technical limits due to the physical location of the battlegroup servers, but I don't buy that, and I hope we will get a proper answer soon.