Interesting new paper (anyone have a link to an ungated version). Abstract (emphasis added):
Would you make the same decisions in a foreign language as you would in your native tongue? It may be intuitive that people would make the same choices regardless of the language they are using, or that the difficulty of using a foreign language would make decisions less systematic. We discovered, however, that the opposite is true: Using a foreign language reduces decision-making biases. Four experiments show that the framing effect disappears when choices are presented in a foreign tongue. Whereas people were risk averse for gains and risk seeking for losses when choices were presented in their native tongue, they were not influenced by this framing manipulation in a foreign language. Two additional experiments show that using a foreign language reduces loss aversion, increasing the acceptance of both hypothetical and real bets with positive expected value. We propose that these effects arise because a foreign language provides greater cognitive and emotional distance than a native tongue does.
As a trilingual, I would still advise against doing learning a newer language for the sole sake of gaining rationality skills. There are much better and cost-efficient ways to improve rationality besides learning a newer language, which would likely take years, or depending on the language, decades, to fully master.
To answer your question, strangely enough, now that this topic has been brought up, I do have a slight change in personality whenever I switch to a different language conversationally, although I might have to experiment further if it affects whether I am more or less rational.
It also happens to me.