I was able to learn Swedish in the ideal way (For an adult) – 3 months of 4-8hrs a day learning vocabulary and grammar and then moving to Sweden and speaking nothing but Swedish for 6 more months – voila! I felt pretty comfortable and fluent by year one, even though my vocabulary was limited to pretty common, everyday conversations. After a second year in Sweden I was totally fluent and learning 8-10 new words per day.
It has been 11 years, but I still occasionally even dream in Swedish.
I know most people can’t do it this way, but if you really want to learn a language, find an intensive program and live in the country for some period of time.