Before I answer that question I will also give you some of my history. I'm originally from Quebec. I did all my primary and secondary schooling in Quebec. I was unilingual. I started my civil law degree at the University of Laval strictly in French. I moved to New Brunswick because I wanted to study common law in French. At the law faculty where I was studying, everything was in French.
I started working for the Court of Queen's Bench. At the time, no one understood my English: I was barely bilingual. It gave me an opportunity to learn English. The desire to practise in the province helped me learn English and speak it increasingly. So I understand the dilemma it causes. A sensitivity to language, even though it is not mentioned in legislation remains an asset in the choice of a Supreme Court justice. We shouldn't delude ourselves. Mentioning this criterion could be an incentive for individuals aspiring to be Supreme Court justices, it would urge people to broaden their horizons and learn the other language.
I personally lived in New Brunswick and was living in a bilingual environment, in Moncton, where 40% of the population is francophone. My parents lived in the city for a few years and were never able to learn English; they lived in French the entire time. It's a matter of will and of knowing that it is a prerequisite. For instance, in New Brunswick, bilingualism was not formally mentioned as a requirement, but because we didn't know the language of our clients, bilingualism was necessary. So, I learned English.