The interview is pretty easy, relaxed. You talk for about 10min, then you get asked a few words to explain in english. The next part is demo classes, you give 2 classes to fake students. Here it is important to prepare a bit, and it has more to do with how you should behave as a teacher and your time management skill rather than knowlege of english. So if you pass the first part, you'll probably pass this too. Just give yourself a few days to prepare.