When i talk italian with Italians, I gesticulate – but not in the presence of non-italian.
Anyway, the cultural influences coming from other languages do not mean that one will develop multiple personality disorder! It’s surely not pathological.
Multilinguals have a double or multiple cultural reference system. That’s all. Our personality and identity is made of many elements, in a world where more and more people grow up and live with various cultural references – even more so after the expansion of the internet – it is meaningless to stick to the monistic concept of identity. "Identity can be multiple, it can be plural" - Tokuhama-Espinosa, T. (2003), The multilingual mind: Issues discussed by, for, and about people living with many languages, Westport, Conneticut: Praeger Publishers, p.185).
Multilinguals do not necessarily have an identity crisis because they are a part of many cultures. If they have a sort of „identity crisis“, then it’s because other people ask them to choose one of their cultures.
When we speak different languages, we also express different kinds and aspects of ourselves. This depends from our audience, the situation etc. In every language we speak, we create different kinds of self-expressions and experiences for ourselves.
Let’s make an example. I usually talk English, but sometimes, I switch to Spanish. Usually this happens, when I’m tired. When this happens, I feel different. My expression changes, words come out much faster and I start gesticulating. But when I talk Spanish or Italian in a more formal context, I slow down and do not gesticulate so much. Therefore, in my opinion, the "personality shift" has a bit to do with the language, but not only. I would say it is like wearing another mask or glove. Sometimes, during role plays I do change language or I do imitate a strong accent in French in order to "feel" and accentuate the difference of the character.
What do you think about this topic? What is your experience as a multilingual – or parent of bi- or multilingual children?