Although strictly speaking it is not a question to me, I'd like to comment. I'm pretty sure, if someone who is not mental sees "behaviour" or "centre" instead of "behavior" or "center" that he is used to, he is not gonna go "OMG, this person is such a godawful speller, definitely not a native speaker". Well, I have certainly been corrected by ukrainians and chinese on those ones.

Ramil, simply take any fairly well-known fiction book by a modern British or American writer and read it. That will do the trick, after all, they can't be that bad. Otherwise, drop your communist beliefs and come on over to an English-speaking country. You'll pick up those nasty articles in no time.