Struggling with a foreign language is practically the definition of mental strain: what is the word for "screwdriver" again? did I produce that "ĥ" sound correctly? are they laughing with me or at me? And mental strain, according to post-rational theories of the mind, has consequences for how we think. But what consequences? Maybe (1) the extra work of a foreign tongue makes people more reliant on unconscious, automatic mental processes (since they used up their conscious reasoning power trying to remember the ablative-honorific form for postcard). On the other hand, maybe (2) the conscious and deliberate effort required by the foreign tongue brings the subject of the words into conscious focus, making people less reliant on those unconscious mental mechanisms. So which is it? This paper, in the current Psychological Science, offers a nice, clear decision in favor of option 2: People who evaluated risk in a foreign language, it reports, were more rational and accurate than those who worked in their native tongue.
Boaz Keysar, Sayuri L. Hayakawa, and Sun Gyu An put 368 students through an exercise devised to neatly separate the workings of what Daniel Kahneman calls System 1 (automatic, unconscious, biased) from those of System 2 (the deliberate, conscious attention that you focus when and where you feel the need). System 1 works with a set of rules of thumb that don't align with logic, one of which is a much greater sensitivity to possible losses than to possible gains.
So most people, if they could give an experimental medicine to 600,000 people and be sure to save 200,000, would prefer that option to a different drug that might save everyone but might not work on anyone. (A sure 200,000 saved is better than a potential to save 0.) However, consider that same drug (could save all, could save no one) against a different alternative: A medicine that is sure to leave 400,000 people dead. In that case, people prefer the drug that might save everyone (potential to save 600,000 is better than certain loss of 400,000). That's not logical, because that drug is the same as the one that for sure saves 200,000. But it satisfies System 1's bias against risks that could lead to a loss.
So the two versions of the question (certain life for 200,000 versus certain death for 400,000) can reveal whether a group of people is using System 1 or System 2 to think about the issue. System 2 users, thinking deliberately and consciously, will tend to see that the questions are identical, so answers to either version will tend to be the same. But people leaning on the unconscious System 1 will show a big difference: They'll favor the save-200,000 option much more than the lose-400,000, not noticing that they're the same.
Keysar et al. ran this diagnostic procedure on 368 students in different settings (native English speakers who spoke Japanese as a second language; Koreans who spoke English; and another set of English speakers who had learned French). The results are pretty striking: In all three experiments, people working in their native tongue showed a strong preference for the option that reminded them of lives saved over the one that reminded them of lives lost. But people working in the foreign language didn't distinguish, presumably because they had reasoned it out and saw that they were the same.
All in all, a fine argument for foreign-language learning, and foreign-language use. More immediately, the study seems to help resolve a question where post-rational models seem to clash. At least when it comes to language, it seems the effect of bringing conscious focus to a subject outweighs the effect of adding to the mind's cognitive load.
Keysar, B., Hayakawa, S., & An, S. (2012). The Foreign-Language Effect: Thinking in a Foreign Tongue Reduces Decision Biases Psychological Science, 23 (6), 661-668 DOI: 10.1177/0956797611432178