It's both EU and US as there isn't another option other than Russian. Can't comment about dominion etc events since haven't done them since coming back to play. The game however, is more populated during night time for me, which is morning/day time for US players. I recommend giving it a try and see yourself rather than rely on replies in here. If you liked Allods back then, the game itself is still as beautiful as it was with lots of new things.
If you aren't a fan of spending cash in the game, it will be cheaper to play the subscription server Smuggler's Paradise but you'll lose whatever item shop goods you have had. But you will level faster and gain some item shop stuff via questing for free, if I have understood right by reading other ppl's comments.
If you join New Frontier server, which is the f2p, you'll have everything you had before you quit. Depending how long ago that was, your mount probably is outdated and gears and glyphs naturally since lvl cap increased to 65.
There will be multiple languages in zone/world chats since some most popular languages are supported but there are plenty of people using English.
Lastly: remember to transfer your account - it may take days or it might take weeks but don't start a new toon while waiting as you can only have 1 account.