The three-page letter, dating from 2011 but only recently released under federal access to information laws, makes the case that bilingualism is ensured through legislation that requires three Quebec judges on the Supreme Court and 15 for the Federal Court and Federal Court of Appeal.
The question of whether the nine judges on Canada's highest court should be fluent in both official languages has been bitterly divisive.
The Harper government has defended its appointment of two unilingual English judges to the high court, saying that judicial competence should be the overriding factor.
Nicholson's letter —the recipient's identity is censored — expands on the reasoning of the government, which faces having to replace two more high court judges in the next two years.
The laws that guarantee Quebec judicial representation "ensure that the bi-juridical and bilingual traditions of our country are recognized and reflected in the composition of these federal courts," he writes.
"However, the overriding consideration for all judicial appointments, including those to the Supreme Court of Canada, is merit, based on legal excellence and personal suitability."
That collegiality is rated high should come as no surprise.
Supreme Court justices work long hours in a largely confined and rarefied setting. The path to a Supreme Court ruling usually starts with a closed-door meeting of the justices to discuss an appeal they have just heard, to air their differences, and to come to a broad conclusion.
Out of that conferencing, the judges decide who will write the court's decision, and if necessary, the dissenting minority opinion.
Creating a high court that reflects Canadian diversity has, at times, been a thankless task.
The government recently came under fire for its most recent Supreme Court appointment: the fully bilingual Richard Wagner from Quebec.
That's because Wagner's appointment reduced the number of women on the Supreme Court to three, the lowest in years.
Nicholson's letter touched on the gender balance as well, indicating that bilingualism is but one of several factors in creating a diverse court.
"The government is committed to ensuring that the Supreme Court is reflective of the society it serves, and places great importance on ensuring that issues of gender balance, diversity, bilingualism and regional representation are carefully considered," it states.
Prime Minister Stephen Harper was criticized for appointing unilingual Ontario anglophone Michael Moldaver to the Supreme Court in 2011, and for his appointment of unilingual anglophone Marshall Rothstein five years earlier.
The NDP has unsuccessfully proposed legislation that would have imposed a mandatory language requirement for new Supreme Court judges.
At various times, MPs have taken swipes at Moldaver and Rothstein because they can't speak French.
In 2010, retired Supreme Court justice John Major returned fire when he spoke strongly against the need for mandatory bilingualism in the court, saying it would disqualify most qualified candidates — especially in Western Canada.
A patient lying on an operating table likely doesn't care if his surgeon can speak both French and English, Major said.
Harper was also heavily criticized last year for naming the unilingual Michael Ferguson to the office of auditor general.
The NDP has proposed a new bill that calls for 10 senior officers appointed by Parliament to be bilingual.
The bill, which is to be debated in Parliament this fall, would include the auditor-general, chief electoral officer, privacy commissioner and commissioner of lobbying.
In his most recent report, official languages commissioner Graham Fraser noted controversies surrounding the appointment of judges and the auditor general.
"The controversy surrounding the appointments has shown that both English and French-speaking Canadians have greater expectations," Fraser said last month.
"The bar has been raised. Canadians expect senior officials across the country to be bilingual."
The next two Supreme Court justices that Harper appoints will most certainly be fluent in French and English because both will come from the province of Quebec.
Justice Morris Fish retires next year, and Justice Louis LeBel will reach the mandatory retirement age of 75 in 2014.