Country is -Japan Nationality is - Japanese Language - Japanese You would say "I am a native Japanese speaker" or "I am a native speaker of Japanese" For the American example- "He is an American and he is a native English speaker"-you would want to distinguish between the nationality of the person and the spoken language because of the complication of the native people of America-the First Nation people. Similarly, i it were an Australian or New Zealand national "He is an Australian who is a native English speaker" or "She is a New Zealander who is a native English speaker" Hope that answers your question :)

I am Japanese. = most natural. I am native to Japan. = less natural. I am a native Japanese speaker. = less natural. ~~~A: Where a you from? ~~~J: (I'm Japanese.) or (I'm from Japan.) ~~~A: So do you speak Japanese? ~~~J: Yes, fluently. (Japanese is my first language.) or (I am a native Japanese speaker)