You can say "저는 한국에서 영어 교사가 되고 싶어요." \^o^/

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"

나는 한국에서 영어선생님이 되고 싶어요.