Scientific American magazine published an article about how speaking various languages can alter the personality of the speaker:
This is true!
I most definitely feel that my character shifts depending on the language I am employing. When I wrote about famous female polyglots, Famous Women who speak foreign languages, Do you know of any?, I was at first surprised to find out that there were so many actresses who speak other languages. But the more I thought about it, the more it made sense. Actors have to get in the skin of another person and pretend they’re from that person’s culture and background. They are perhaps one of the most naturally gifted pools of language learners because it’s easy for them to pretend to be someone else. When learning a language, we have to live the language and inhabit the world of the language to blend in the best. As a result, we change.