Like Bryan Caplan, I think that most investment in learning a second language is a waste. Yes, I've benefited, when traveling abroad, by knowing some French (learned from 8th grade through 12th grade plus first year of college, all in Canada) and a smattering of German. That's the benefit. It was small. The cost, however, was substantial.
When I was on KGO (a San Francisco radio station) a few years ago (circa 2006) to discuss that day's 400-point fall in the Dow-Jones Index, I pointed out that at the time it was about a 3% fall. Various financial pundits were saying that it was due to an even bigger fall in China's stock market. I didn't know enough to comment on that. At the end, one of two hosts asked me, "If you were giving a 12-year-old American kid advice on what languages to learn, what advice would you give?" I think he was expecting me to say "English and Chinese." I answered, "Two languages: English and math."