

This is a shockingly common view of this movie. In fact, most media that features a villain protagonist tends to have this problem. Look at Breaking Bad, Fight Club, or American Psycho.
They present the reasons why the villain makes the decisions they do, in a way that is sympathetic to the audience, then it turns into a bit of a power fantasy before their fall at the end. A lot of people seem to look at the power fantasy portion as fighting against an unjust world, rather than an abuse of normal people.



The real answer is rough, because there are no shortcuts.
The best way to do it is the same way you learned your primary language. Learn just enough through study to be able to use a little bit of the language, and then actually start using it.
Talk with people who speak it, and learn to read and write all over again. Sound like a tourist for a couple years as you pick up more and more. Eventually you’ll be fluent.