I have my own very French way of using the English language (forgive me for that, I've always kinda felt bad for the reader), a language full of lil mistakes.. but the English language has become so much part of me that when I think about something, it naturally comes in English first, most of the time! In my mind, I talk to myself in... English! lol
(whaaaat? you never talk to yourself? a pity! one of the best company you can find! Very supportive :P)
I used to find that very disturbing! English is not my mother tongue, I don't tame it perfectly at all, I don't live in an English-speaking country (far from that really! lol)... so I can't explain why it happens, but I now live with it in a most natural way.
I've noticed that French language comes more easily when it comes to food, to deeper thoughts, like when talking politics or literature for instance, English comes naturally for sex, slang, fast reactions, anger, desires, feelings (probably why I keep blogging in English now. I'm not a deep thought kind of person :P)
Well, when I gotta explain something, defend a point of view, French comes first. When I describe my paintings, much easier in English to me.
And by the way, I have my third (not so) hidden language: my hands making doodles! yeahhh! so cool!
I truly think you don't say exactly the same when using one language or the other. My own sensitivity adapts to what fits me. That's really practical.
I wish I knew 5 other languages, including music, and would switch according to what's the most appropriate!