The previous threads noted by anhnha are helpful.
I would just add that if your examples represent the complete sentence (i.e., you are not adding anything else to the sentence) then I would only say "My English has improved."
The word been gives a little more emphasis to whatever the driving factor in the improvement was, but as others mentioned on the previous threads, when an object is added to these two sentences, there isn't much of a difference in the meaning (with other verbs, the meaning can change).