Speaking both French and English can get a bit messy, but it can also be a lot of fun.
I was born in France and lived there for the most part of my life. I have the frenchiest of names. I'm not big into striped shirts, but I could easily switch to a cheese-only diet if given the opportunity.
A few years back I went to live in the US. At that point I knew some English from school, but never actually used it in real life. Also, my accent was terrible. After a while I got better at it even if I never got the accent quite down. However to my amusement I could pass for American with French tourists asking for directions in Times Square.
So really I think that the English language is very interesting as well. I wouldn't say that I love it as much as I love French, but it's a close second. We can say that it's because I'm annoyed about the fact that I can't be perfectly billingual.
For the record, I got back to Paris in 2009 so I've lost a lot, so please bear with my written English on this one. I'm sure talking about mixing languages while writing poorly constructed sentences will sound silly at some point, but hey.
The thing is during my time abroad, I started to mix the two languages in my head. In some cases a word in French would come up, sometimes in English, and then, depending on the situation, I would translate it approprietly.
I've been told that you know you can speak a language when you dream in that language. To be honest, while I can sometimes remember the subject of my dreams, I never know what language is being spoken. Same goes for articles that I read online, I'll remember the facts but often forget if I read them in French or not. Of course right after I'll still have some memory of it, but a few months later some information would stick but the language behind it gets blurry if there wasn't some memorable quote in the text.
While staying in New York I met people that would speak English but also some French. This was really a lot of fun since we could just switch back and forth between languages as we felt, picking the most fitting words to communicate. The novelty of doing that wearing off, I realized that it was really the perfect way to go for me. In each languages there are concepts that you can't express in the other... or at least not a specifically.
For instance let's take "whimsical". WordReference would say "Fantasque", "Capricieux" or "Saugrenu". To me it doesn't work, this is not what "whimsical" is at all. There is just no way to capture the essence of this word in French.
Here is a conversation I see myself having all the time:
« Hey! How do you translate X in French/English ?
- You don't !»
And I'm not just being annoying. This is quite true that you wouldn't say some things this way. Languages tend to lead you in a direction when it comes to constructing sentences and sometimes even your reflection changes when thinking with a given language. If you write something in X and translate to Y, you lose the soul of the text.
Obviously you can do some clever translating, but without moving huge blocks of ideas around, it won't sound good.
Back In France
When I got back to France I kept this habit going with some friends of mine that could follow such a way of speaking.
The problem was with the others. When unable to use English to complement my French, I would end up stumbling on words, losing track of what I wanted to do... and overall feeling like I couldn't even speak French! Sometimes it could get annoying because France loves to make fun of people mixing languages. The perception of such a person is either that the guy is really smug or just an idiot.
As time passed, my English got worse since I didn't get any practice, but I still had this mixing issue. This felt weird because I didn't get to speak English everyday anymore, but if you look at my situation it makes sense. My job as a developer requires reading a lot of documentation always written in English with terms that don't even exist in French. Once this is done I get to write code, bug reports, emails... all that in English.
While I like listening to podcasts in French, I mostly find my content in English. Same goes for reading, I like novels written in French, but most of the blog posts or in-depth articles that I read will be in English. Same logic goes for movies, shows, songs...
All this seems to keep the confusion alive, even if I don't speak the language.
In the end this isn't a real problem for me. I'd much rather be understood by more people than be perfectly eloquent for less people.
It has downsides, but it often consists in me having to repeat words again in some situations. I manage to mostly use French words and only add English when there is no good translation available. If the person I'm talking to is not confortable with this I can shift to speaking only French - I'll just take a couple more seconds to translate in some cases.
Maybe sometimes people will think that I'm an idiot, or that I'm smug... but I don't mind.
I grew to like the process of finding the best way to say something from two sets of words instead of one. It allows me to expand the way I can express a concept, convey an idea or construct a sentence.
... and if they get to do it in Quebec I don't see why I couldn't either!