the best way to learn the language is to throw yourself into a country where it is spoken....that way you will be forced to learn it....and learn it well, especially if you are younger. It took me about 2 months to master English (for a 4th grade level) when I was ten, not having been exposed to it previously....now 12 years later the problem is remaining fluent in Polish.
It is most likely the best way for children.
Another is to limit your language requirements, hands, grunts, and cussing help a lot. There is always ubiquitous f**k which is always very helpful.
Failing that check yourself to prison (pick the country you want to learn the language of). Admission is not easy, but not impossible. Make sure to commit crime giving you sentence suffiniently long to master your skills. Do not let people to fool you, you will need at least 3 years (I will recommend 5). Also choose the place where prisons are bearable. See the world and make new friends. Good luck on the new way of life and keep in touch.