Happy people live minimally, tell the truth, never make excuses, take time to listen, don't hold grudges, speak well of others, choose friends wisely, establish personal control, dream big, see problems as challenges, nurture social relationship, avoid social comparisons, treat everyone with kindness, exercise, don't sweat the small stuff, accept what can not be change, meditate, avoid seeking approval from others, express gratitude for what they already have, eat well, wake up at the same time every morning, and get absorbed in the "now".

La gente feliz vive mínimamente, dice la verdad, nunca poner excusas, toma tiempo para escuchar, no guarda rencores, habla bien de los demás, elige buenos amigos, establece el control personal, sueña en grande, ve los problemas como retos, cultiva las relaciones sociales, evita comparaciones sociales, trata a todos con bondad, el ejercicio, no se preocupa por las cosas pequeñas, acepta lo que no puede cambiar, medita, evita la búsqueda de aprobación de los demás, expresa gratitud por lo que ya tienen, come bien, se levanta a la misma hora cada mañana, y se absorbe en el "ahora". 

Well, the answer is may be =D True is, that a person who speaks more than one language, feels part of the different cultures and acts in different ways. In my case, when I talk Spanish my accent is different if i'm in Argentina, and i talk very andalusian when i'm in Marbella.
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.

Multilinguals often feel different when they are switching between their different languages. But the difference is felt during this shifting, because the culture, the frame of reference changes with the language too. François Grosjean describes it like this: "what is seen as a change in personality is most probably simply a shift in attitudes and behaviours that correspond to a shift in situation or context, independent of language" (François Grosjean,Life as a Bilingual: the reality of living with two or more languages, Psychology Today, 2011) – I would add: but triggered by the change of language.

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?