Here are some common mistakes Koreans make in grammar:
1.) eye shopping - referring to window shopping
2.) What mean? - the correct way to ask this is... "What do you mean?" or "What does that mean?"
3.) I will going to - "I will go" is right. "I am going to " is also right but don't use them together.
4.) arbeit - I often hear this and they actually mean "part time job"
5.) I think that! - when you agree with the other person, you can say... "I thought so too" instead of saying "I think that"
That's all for today! Till next post!