I had the same problem when learning Japanese. Whether teachers or friends, I didn't often speak it with other men, and definitely picked up some softer turns of phrase and pronunciations.

Once I became able to hear this in myself I started overcompensating somewhat, and had a few people comment that I sounded unusually brusque or was saying something almost cartoonishly masculine.

I don't think there was anything inherent in the language that changed my personality, but it definitely added another layer of concern and thought to how I interacted with people. A lot of it also had to do with just the more limited set of words available to me, though. Maybe I wanted to say something snarky or yell at a taxi driver or whatever, I might just not have known how.

Ha, that's funny, I thought I was the only one. I have noticed that when I speak English (to my wife and daughter) I speak in a higher pitched voice. As soon as I switch back to my native Dutch, I drop to a lower pitch, because to my ear it would sound ridiculous otherwise.

Some years ago I spent a few months in Brazil. My Portuguese was barely conversational, so I had to pay very close attention to vocabulary and usage to understand anything. I noticed that women had a distinctly different vocabulary from men. For example, men had one word for dog and women had an entirely different one, not just the "dog", "doggie" distinction. Talk only to women and you end up talking like a girl, :-)

I live in Poland and practise most of my Polish with my girlfriend. This has caused the same effect, with most of my slang being very girly. It's an interesting position to be in...