> I always thought that two near-monolinguals dating or getting married would be the quickest way to learn a new language, although I never had a chance to test this hypothesis

They have an expression for this in French:

"La meilleure façon d'apprendre une langue est sur l'oreiller"

"The best way to learn a language is on the pillow"

I saw lots of other exchange students improve their French immensely when they started dating a native. My experience was that having that sort of language partner is nice because they're sympathetic to your mistakes and there's lots of built-in incentive to have more interesting conversations.

I learned French almost entirely by helping raise my (now ex) girlfriend's 6 year old son. Best teacher I could have asked for, and he wasn't even trying to teach me :)

She was also very helpful as she was a native French speaker, but fluent in English.

I did this. I lived in Ecuador for a year as a kind of sabbatical (though I'm not an academic.) Before I went I took a 6-week Spanish 101 class so I wouldn't starve, and then just muddled along as best I could. After about 3 months I had the basics down. I could ask for and follow directions, buy stuff, read and write business email, and have a conversation with someone. But socializing was hard - a conversation that involved more than one other person left me wondering what was going on, and I couldn't figure out how to say things fast enough to contribute before the the topic had changed. Also, I didn't consume media like TV or newspapers because it was too much work.

Then I started dating an Ecuadorian woman, and my Spanish acquisition just took off, especially when we moved in together. Like the Korean, I put in a tremendous amount of effort, although without flash cards. I did repeat everything over and over, to make sure it stayed in my head. But mostly it was just the endless necessity of communicating on a practical and intimate level about everything.

"Where's my blue shirt?" "Why is your friend angry?" "What's this letter from the electric company about?" "When I was a kid, my grandfather gave me a baseball glove for Christmas." "No, I wasn't looking at that other girl." "There is corruption in the U.S., it's just more sophisticated than in Ecuador."

The other important thing that happened was that I started watching TV with her. She was really into telenovelas and sketch comedy shows.

Let me tell, you telenovelas (spanish soap operas) are awesome for learning the language. First, the characters all have accents that convey their social position, and different novelas are made in different countries. So you get exposed to a lot of variation in pronunciation and vocabulary. On the other hand, this is TV, so everybody enunciates clearly and there's no hemming and hawing. Finally, everything is so dramatic and over-acted that you can tell what's going even without understanding the dialog. I alternated between rolling my eyes and concentrating furiously to catch all the nuances.

After a year, I was pretty much fluent in Spanish, though not quite at the level of the Korean's mastery of English. I have an idea of what kind of effort would be required to get to that level, but since I'm not in Ecuador any more, I haven't bothered. My wife and I speak both English and Spanish around the house, but we try to keep it to one language at a time - not always easy.

So yeah, marrying a Spanish speaker was an enormous aid to learning the language. I don't know if it was the "quickest," but it was definitely faster than doing it on my own, and much more pleasant. ;-)

I always thought it would be difficult to have an intimate relationship with someone you weren't already fluent in the same language with. How do you even arrange that?