I've noticed that I've recently started to dream in German. Well, the people who pop up in my dreams are speaking German, and I seem to understand them and act accordingly, but I never speak in German in my dreams. Actually, I rarely say anything aloud in my dreams anymore; probably a reflection of real life.
The interesting thing about this is that I don't speak German. Well, I can utter a few words or phrases here and there, and my comprehension of spoken German is growing, but I don't speak it myself.
Oddly, even though I still have a fairly decent command of the Spanish language, I don't recall if I ever dreamt in Spanish. I never lived in a Spanish-speaking country but I did -- later -- live in a Spanish-speaking area of Manhattan (it might surprise you to learn that much of Manhattan consists of those who speak Spanish as their first or only language, except for the wealthy areas, where English is the primary or only language spoken). Although in Manhattan, I was hearing Dominican Spanish, which was very different from the Spanish I spoke: Madrid Spanish at first, then Mexican Spanish (both due to my teachers and friends), and later, when in college, I added Colombian Spanish to my repertoire (thanks to my two Colombian roommates).
Even though I did live in Tokyo for a little while, I didn't dream in Japanese when I was there. I learned Japanese much more quickly than German, thanks to my labmates, colleagues, and mentors, so I imagine this disparity is a matter of time: I did not live in Japan long enough to actually start dreaming in Japanese.
But my dreams have not been limited to languages I've been surrounded with for a long period of time. For example, when I took calculus classes, I dreamt in calculus, often dreaming the solutions to "problems" I had solved during the day .. those dreams were fantastic episodes like something you'd see in an art museum, Dali, Escher, Hopper and other painters whose names escape me at the moment. Much better than drug-induced visions, those were some of the most fascinating dreams I've ever had, in fact. It makes me want to take a calculus course again, just for the dreams I had.
So this has led me to wonder what my mind is accomplishing by dreaming in a language I don't speak? And in a bigger sense, I wonder what is the purpose of dreams at all? Do animals dream? (I suspect they do, based on my observations). If so, what function do dreams perform in their lives? I know a lot has been written about this topic, but what do you think?