I have met many people who have lived in North America for over 10 years, and still speaking the same kind of Chiglish (Chinese English). In fact, only perhaps 5% of people can really change their pronounication habit. People who can will do it in the first five years, and those who can't will never be able to do it. I used the word habit because I know how hugely different it is to make each and every English sound than using our Chinese speaking habit, even for words as simple as "it is". Unfortunately, most of our Chinese people have not come to realize that, and thinking they are doing just fine.