Growing up, the foreign languages to learn were Russian and Japanese.

If I had it to do over again? I'd go with Mandarin and Spanish. With Mandarin, you can more or less communicate as necessary anywhere in Asia, while I far and away prefer Cantonese, it's really only useful in HK. As a Californian, I really regret not learning Spanish and wish even now that I can speak it.

Traveling to a place where one's fluent in the local language makes all the difference, at least for me. If one can't speak Cantonese fluently in HK, you'll never experience the full flavor and richness of that city. Likewise, I'm starting to feel as I'm missing out on something in my native California never having learned Spanish. When I was growing up, I never really realized or appreciated that many of the names of our cities were Spanish! Monterey, San Francisco, Los Angeles, El Camino, etc...

As another post said, reading French/Italian/Spanish isn't much of a challenge, especially for anyone whose studied Latin, but speaking French is whole other story. In my view, it's the most beautiful language of them all, but no matter how hard most try, you'll never speak it the way the French do.