I want to study English intensively, it´s my goal to get improving and improving, until I become proficient in the long term. Then I will communicate with others in that language confidently and effectively.
You could stop at the period after "long term", though.
To kis (keep it simple) and piggybacking on your sentence:
I want to study extensively to improve my communication skills/fluency/proficiency in the long term.
And there are other ways to express that...of course!