Speaking foreign language like a native...?

Hi, I'm Native Korean speaker in South Korea.
Nowadays, I'm enjoying the TV Show entitled '비정상회담' which might be translated as 'The Unofficial Summit Conference'.
The men who appear the show who are from Turkey, Canada, Italy, U.S.A., Australia, Ghana, China, Japan, Velgium, France and England. But James from England is has gone aborad for his study, so a new face will be appeared from be appearing next week. But However, it that is not important. When I watch the show, I feel so funny, but I also feel amazing amazed what that they only communicate by with Korean language almost perfectly. How did they? Some of them speak Korean like a native. Absolutely. Does it sound like a native language to them? Perhaps, but I don't know because I have no experience of the kind like that. If you have a near native command of foreign languages, please tell me how it feels to be that way. I hope you put write many comments.