I find that I am having a different personality in each (3) languages I speak, especially in context in a different country. When I switch back to my original language to speak to someone in said country my habits I do in my original country come back for the part and then I revert back. Feels a bit schizophrenic, but I think it is normal for most people. My child is showing similar patterns.
To me this is proof that learning a language touches a lot of parts in our brain, not just affect the parts about learning
I don't think it's just language. I remember having this happen just by having separate groups of friends. You end up in a situation where the two friend groups meet and suddenly realise that you are two different personalities and that you don't know how to act.