NPC/Monster Names, Skill names, Stats, Item Names, some dialogue (randomly), some of the options when you have to select something.
If you probably have memorized it in SG/MY, things in idECO won't be so bad.
Also, the players there are really nice, and if you need to talk to them, just say you speak English and so will they. xD
If you're reading this, I'm currently playing @ Grand Chase Reborn
IGN: Eucleides | Feel free to join and add me!