uchegod: if I understand this correctly, you gave your post to somebody else for correction and they posted it as if it was theirs.
No it has not happen. It was what I am thinking to do. I want to know if is a crime first.
Well, the definition of "crime" varies. What I would be worried about is if it's ethical to do so.
Personally, despite practical considerations that have been stated before, I think using somebody else's work without their consent and not giving them due credit for it is morally repugnant.
You can learn before, and then do your own work. The whole "my English is not good" excuse is BS, in my opinion. Like I said before, there's a whole lot of people here whose English is far from perfect (including me), and we go from taking forever to carefully craft each post, to just do their best and let other people to deal with it.