If you learn about polite expressions, those answers are not problem.
casually, you can say "한국에서 영어선생님이 되고 싶어"
Explanation.
First, you can omit the subject, that's why i didnt put "나는" or "저는"
Second, most korean don't use to say "남한" ,which stand for South Korea, So you can say "한국"