Not happy about my English at all

I have lived in New Zealand for about three years now, and I might can not say "I can not speak English" any more.
I can almost understand what people say and can response to them, but I am still not good at explain about things which I have done or happened.
I mean I can do short responses but can not talk longer, and writing as well. 
I am recently stuck and have totally no idea how to improve my English more.
I always make same mistake over and over, although read some books, I can not use new words. I may copy them?
All new words pass my brain very quick. Or even though I know the words, I do not know how to use them, that is the problem.

Today I watched an American movie with George, it was a comedy and must be fun, but unfortunately I could not understand their English any more.
What did it mean? American English and Kiwi English are different?
I was thinking English is a international language, however it was quite shocking that I did not understand anything.

I am really interested in study English and it will never end in my life.
I am trying to avoid to use Japanese ( it is a lie! I do mixi=Japanese social net work, too much.) I still want to avoid Japanese seriously until my brain become "EVEN".
Now my brain is 85% Japanese or more. I really feel old. How long have I used Japanese!? more than 50 years, half century! I am really really not happy about my English!