My grandmother, an immigrant from Lithuania, spoke fluently and read 6 Eastern European languages. She never was able to speak English very well. She could not read it.
My mother, aunt and uncle speak flawless American English because the old lady told them they were in America and needed not only act like Americans, but to be Americans.
I will never fault anyone who can't speak good english as long as they are trying and understand that they are no longer what they ran away from. If you left a place and came to America and refuse to assimilate, then what are you?
You are certainly no longer what you were, as you have left that; turned your back upon it. You are not an American because you refuse to be one. To hang onto the culture you left other than to appreciate your roots, is to be playing false to your ambitions which drove you from that culture. To refuse to become one of those that make up the place you yearned to come to, calls to question the value that you bring to your adopted land.