Internation Rohan and Ijji uses the same server to play. So basically your friend can play on International and you are playing on Ijji, you both can still play together.
The RP(cash currency) cost the same though. The amount of Ijji coins you use to convert into RP is proportional to International RP rate.
Why there is an Rohan is Ijji, I don't have a blues clues.