I'd say it depends on your goals. Spanish and German have the practical advantages you and Jon mention. Travel and business aren't priorities for us. Instead, we chose French because (i) I speak it reasonably well and so can help more, (ii) reading French is an important academic skill (same case could be made for other languages, but French for what my dc is interested in is the best case), (iii) I always find it embarrassing when educated people mispronounce French (or German, actually, so dc will take both -- French and to a lesser extent, German, terms are ubiquitous in some fields). Probably you could make a similar case for many other languages, but given dc's status as a humanities kid focused on English and French literature and history, French and later German fit for him.