It's an international server, which means, that the basic language is English, but the players can find there people from their own land,too.
Infinite Aion has different servers for playing available:
1 Low rate server
1 High rate server
1 PvP server
and 1 Test server For development, but players can play and test there as well.
The private server is free to play, and requires the current Aion retail patch state on your PC + the Infinite Aion Launcher.