From my experience there and seeing the litigants argue in French, I never had the impression that they did not feel they were being fully understood. There will always be, of course, the three Quebec judges, but the environment and the translation is such that it never occurred in my 14 years. The translation is very good. The parties argue in French and seem quite comfortable with the questions asked, and in many cases the lawyer understands English, so he answers; in other cases, it's translated for him.
On June 17th, 2009. See this statement in context.