Concentrated learning for English accents is effective. From personal experience (through acting) I can tell you that sitting down with a professional accent co

Concentrated learning for English accents is effective. From personal experience (through acting) I can tell you that sitting down with a professional accent coach 2-3x per week can have you speaking and understanding heavy, hard accents (https://www.youtube.com/watch?feature=player_detailpage&v=ZUNfovLWktA#t=65 https://www.youtube.com/watch?feature=player_detailpage&v=ZU...) quickly. A month of lessons will get you understanding, and fooling some people who don't have that accent. A few months is required to fool people who have that accent. From this experience I learned that the process of learning a new accent is totally separate from learning a language as most people do it. You need to master IPA as well as carry a mirror to watch your own lips and have good close-up reference material. As evidenced by all the mediocre accents in movies it's not a foolproof process, but it can certainly get you much closer to your goal.