With English you get to lose nuances and to simplify your thoughts.
As a result, you cannot put exact words on your emotions or your thoughts and you start to think and feel differently (and not in a nicer way).
However: I am kind of a different person when I speak English. My personality changes. Not for the worse though (and that's where I don't agree with the "and not in a nicer way", that's not how it is for me).
The problem is that, as a non-native speaker, the words carry less emotional weight somehow than my native language. This is not specific to English, and it's not because of a lack of familiarity. It's most visible in swear words - I have no problem saying any swear word in English, while I still get slightly squeamish with certain swear words in my native language.
It's basically a part of how you can't really absorb certain cultural aspects of a language, even if you learn about them. They're never going to be a part of your own internal culture if you didn't grow up with them.