How did you really learn a foreign language?
nrr: I took seven semesters of German in high school and managed to skip everything but one 300-level grammar course at university, but I appear more to be the statistical anomaly than the rule.  I'm fluent when discussing matters that are mostly mathematics and physics, but I find myself tripping on several everyday things.I took a genuine interest in learning the language, and I made a point of hanging out with German-speaking folks on IRC (in my case, mostly demosceners) and the like in order to get an idea of how the colloquial language works.  Reading and writing formal and informal German both help tremendously as far as extracurriculars go if full immersion is unattainable, but it's best to supplement that with something like television shows (telenovelas are particularly useful here) and music.In addition to all of this, I had the goal in the back of my mind of earning a PhD in mathematics someday.  That said, at schools in the US, proficiency in one of either French or German (sometimes also Russian and Latin) is often a requirement as it is viewed as an important research skill with respect to late classical and early contemporary literature.I go with everyone else here, though, and maintain that full immersion is the preferred way to fly.