Esperanto. The wave of the future.

The is a great case study in how all tastes and preferences are subjective (i.e., there is obviously no correct answer).

I would still recommend German, if only because it gives the best insight into the structure of English. The two languages have both enough in common and enough that is different so as to make studying German grammar VERY useful in gaining a greater appreciation of English grammar. That benefit outweighs (IMHO) any guesstimate as to which language will be the "hot" language in "Year t+n".

P.S. Latin would also qualify under this paradigm, but it wasn't on your list.

"Naturally I am biased in favour of boys learning English; and then I would let the clever learn Latin as an honour and Greek as a treat. But the only thing I would whip them for is not knowing English. I would whip them hard for that."
--Winston Churchill

German. In the last few years I have spent 2 weeks in the summer teaching in Munich, and it would be great to know the language.

I think about this question every day, as I've studied all of the languages you mention (which has opened some fascinating doors for comparative work). Before you launch into Chinese, you MUST read this fantastically funny and insightful article: Why Chinese Is So Damn Hard by David Moser (Michigan Center for Chinese Studies), http://pinyin.info/readings/texts/moser.html. I gave up on Chinese after trying it and reading this article, though I still find it fascinating and will continue to dabble. As for Arabic, the problem is its diversity, as seemingly every country has its own version (more different than British and American English). If you learn the standard "Fus'ha," you'll sound like Webster (or maybe even Shakespeare) to most natives, and it's a bear of a language, as well. Stick with Russian if you want a fun challenge that will provide lots of interesting comparative company law opportunities. Though it's dated now, I still recommend (and use with some private tutoring students) Ben Clark's textbook on beginning Russian.

As for me, I'm starting Polish now and continuing with Danish, but I must say that I agree with Kip and Orin that German has helped me more than any other language (at least in my law research). For fun, I would choose Greek (koine, not modern).

Your post seems to indicate that you are interested in learning a new language just for the fun of learning it, but it doesn't seem to take into account either the network effects of language (to whom are you going to speak this language) or the practical benefits (this language will help me to do [blank]). I would either pick Swedish (so you can talk to your wife in your own secret language) or the language your son picks (so you can learn it together and have your own secret language) or Spanish (so you can talk to the other half of the people on our continent). Otherwise, the exercise seems more like learning a code from WWII or Braille -- sort of a nice mental exercise.

Fun comments. Thanks.

Christine, you seem to place a very high value on secret languages! I guess I don't have that many secrets. This never occurred to me as a relevant consideration.

But I was trying to think practically. I can get around Europe pretty well with my German and base-level understanding of French. But Beijing was much harder, when I was not with my Chinese hosts. So I figured a little Mandarin might be nice.

Plus you're right about learning a language just for the fun of it. Languages are fun, and I think learning Mandarin would offer some interesting insights into China.

Jason ... wow. Obviously, you agree that learning languages can be fun, but Polish? There must be more to that story. Thanks for the tips, by the way.

Orin, I'm jealous. Munich is a wonderful city. I hope you take the time to do some side trips.

Kip, I thought about including Latin, but we were pretty focused on living languages. Speaking of which, Jeff ... keep riding that Esperanto horse!

Hi Gordon:

I'd pick Chinese or Arabic or perhaps Russian, for a different reason from those earlier stated: language is a really neat window on culture, and there may be more fascinating discoveries to be had with languages and cultures not so closely related to mainstream US culture.

For example, my understanding is that in Chinese, there was no generally accepted word for "democracy" until early in the 20th century. If you wanted to say "democracy," it took at least a few sentences. Conversely, there are Chinese words that have no one-word English translation, because a concept readily apprehensible in Chinese may need some explaining in English.

I grew up speaking Mandarin with my parents, but like many first-generation American-born kids, I stopped speaking it as soon as I hit grade school. I've relearned a bunch of it over my adult life, and so perhaps I have a special fondness for these sorts of cultural discoveries. No doubt, however, that most European languages (not Finnish) are probably easier to learn, though you won't get as big a secret language bang for your buck.

Anksthay, Ordongay.

Personally, I think a law professor should be able to say "conflate" and "normative" in any language.

Ouryay elcomeway, Effjay.

Is anyone aware of more immersion-like programs (that aren't either a million bucks or in the form of a plane ticket)? I learned English around the house, and it would be more valuable for me to just do it than it would to be able to explain verb conjugation academically.