[evanny]

well in my country for you to be a teacher you actually have to study teaching to be one. every teacher i know has spent 4 years in university, then usually majors and only then starts to teach while also attending all kinds of courses once in a while for improvement.

and what you just said are the mistakes i mentioned. but i would not call them major. i would be far more worried if i was thought incorrect grammar than idioms or pronunciation. and usually both of these things are left for the person to fix on his own when face with real life situations. doesn't matter how good the non-native teacher is - everyone still needs to practice with different people to "see" how language works in real life.