Fortunately, English was taught to me early on, so I had a better understanding when I took English courses in middle and high school. I have, under my belt, 6 years of scholastic English study, not to mention the revelution of the internet over the past decade, allowing me to communicate with native speakers of the language, English, American or otherwise. From that, I've learned slang, idioms, vulgarity, etc. that I otherwise would've never learned from a book.