Your last statement assumes that no high school student has ever left the country. Actually going abroad, using what little of the language I knew and having an amazing time were huge motivators. But the biggest was the frustration I felt when I realized how little I knew. In my case I studied Japanese, but by the time I got to high school my interest in anime was already fading and most of it was way too hard for a high schooler to get much if anything out of it. My high school held trips And home stays to most of the languages that taught and nearly everyone I knew that went came back with a huge desire to learn more.