Do you have a different personality when you speak English?

The other day, I got into a conversation with one of the students I tutor. She's from Japan, and has been studying English in New York for over a year. We were talking about how she acts around her English-speaking coworkers. I asked her:

"Is your personality a lot different when you speak English?"

"No, it's the same," she said.

I was surprised to hear that, because most of the people I speak to say that their personality changes a lot when they speak a foreign language. Some people feel more outgoing, some shyer, some more serious. In my own case, I feel like I have a separate Japanese-speaking personality which is more polite, easy-going, and kind of fatherly than my usual English-speaking self.

But why do we have separate personalities like this? Here are two possible reasons:

• We don't have enough language skill to express our entire "true" personalities. 
• We're changing our personalities to fit the culture that we're trying to communicate with.

Of course it's great if you can become fluent enough in English to express your full personality. Then your native-language personality and English personality can be closely matched. But if you're changing your personality on purpose to match the culture that you're dealing with, that's OK as well.

So what about you? Do you have a different personality when you speak English? Do you try to "act like yourself" as much as possible, or do you try to take on the characteristics of other English-speaking people around you?