A few weeks into my Parisian séjour, and I find myself quickly learning the limitations of my French conversation skills. I've found that when a new French person says something to me in French, it takes me a moment to internalize, translate, and react via a spoken response - by which time the person has either assumed I do not speak French or that I was offended by what they have just told me.
What need to work on, I've realized, is the speed at which I can take in an unexpected French comment, translate it, react to it, form my response, and then say it in French. I've noticed that a lot of the french social / café culture hinges on back-and-forth debate, discussion, and clever raparté. Just speaking, just understanding, French (although certainly helpful) falls a little short when it comes to spontaneous and casual conversation. Experiencing the French language in a classroom setting for so long has prepared me well for a specific type of interaction - namely, structured question and response, with the response usually being voluntary. At the quick speed at which many Parisians chat back-and-forth with each other, being engaged and equally witty can be very difficult, and often leads to a lapse into English. Besides just sentence-formation, grammar, and vocabulary, the key and the heart to the French language is the art of speaking. Beyond pronunciation, one's word choice and unique way of conveying a message is paramount.
Through written correspondence with a French friend, this fluidity and sonorité of language has become very clear to me - contrasting starkly with the functional French I tend to respond with. What you are saying must be in sync with the way you are saying it. I'm often impressed by both the beauty and gentle ease with which she gracefully conveys her messages. Impossibly, it is this innate effortlessness and comfort with the language that is so difficult to nail down. It is also frustrating to be unable to translate the exact nuances of what you mean to say or imply from your native language to a new one - especially when it comes to humor, which is easily lost in translation. I think, perhaps, the solution must be cutting out the translation piece and trying to speak directly and solely in French - not comparing your phrase to an English counterpart. The chunkiness that carries over from English will inevitably weigh it down.
Speaking a new language is not just a translation game in which you just exchange one word for another. Speaking a new language (effectively) is adopting a new way of thinking, taking on a new perspective, and learning to express yourself through a new medium with new vocal tools. This grassroots approach adds depth and character to what is being said, while translation keeps ones expressions close to the surface. Challenging oneself to speak French from French and not from English is certainly a more rigorous and immersive process that is ultimately more enriching than the superficial act of translation.