the funny thing about language

To learn a different language from your native language is actually a very difficult thing to do.
However not all people in the United States or even if they live in a English speaking country are able to speak English.
Some very good examples are Chinese who live in China Town or the American troops living in Okinawa. Even though they live/born in a different country and been there for a long time some people can't speak that language and only their own native language.
Also if you don't have any interaction with your native culture for a long time you tend to forget the language and won't be able to speak it any more. So for me I was very lucky to stay in touch with my Japanese culture and deal with my American culture since I was young. Plus probably my motivation when I was learning Japanese and English was to be able to speak with my family and the people around me.