During a visit to Quebec City, the Liberal leadership candidate was asked Thursday by reporters about plans by the new Parti Quebecois provincial government to toughen language laws.
The pro-independence PQ calls the matter urgent, following census data that suggests a decline in francophones' demographic weight.
Trudeau's response: the PQ language policy is unnecessary and counter-productive.
While he expressed support for the old Bill 101, pointing out that it has allowed French to thrive in Quebec and keep Canada bilingual, Trudeau said Thursday that adding teeth now to the language law risks needlessly reigniting old battles.
"I think we are revisiting old debates," Trudeau said in French.
"The majority of people in (my Montreal riding of) Papineau, in Quebec City and across Quebec are focused on their jobs, on the economy, on health care and on the education of their children, in order to participate fully in this era of globalization."
His remarks come as a new poll suggested a Trudeau-led Liberal resurgence in Quebec, a province the party once dominated under his father.
Justin Trudeau's opinion on language to a certain extent echoes the position of his father, Pierre Elliott Trudeau, who brought official bilingualism to Canada and criticized the French-only policies of the PQ.
The younger Trudeau is more supportive of past PQ language policies than his father was. However, the new PQ government has vowed to strengthen language laws, saying it needs to protect the French language and culture.
The PQ campaigned on a promise to extend the law to junior colleges and smaller businesses. It has also proposed applying it to daycare. In the wake of this week's census data, the PQ calls the matter especially urgent.
But Trudeau isn't alarmed by new figures suggesting a relative decline of French in Canada and on the island of Montreal, saying it is the result of demographics and a lower birthrate.
"My concern about reinforcing Bill 101 is that we will find it punishes Quebec francophones who want their children to develop a capacity in English, the language of international commerce," he said. "I don't think this is a good direction."
He also suggested that French is faring better than it used to in Quebec.
He pointed out that while older immigrants may speak their native language and English, their children are becoming fluent in French.
"If I speak to the parents of people from Bangladesh, Pakistan or India, yes, the parents speak English but when I speak to the children of five, 10 or 15 years old in my riding, they're speaking French and it's because Bill 101 works.
"I'm not worried. I'm proud of my beautiful French language."
The remarks earned Trudeau a scolding from the PQ government.
"I'm a bit disappointed by the lack of knowledge he shows of the basic issue," said Jean-Francois Lisee, the provincial minister responsible for Montreal.
"He's saying that Bill 101 impedes francophones' (ability) to learn (English). Well, the majority of citizens in Quebec are bilingual. We are the most bilingual society in North America and that is great. Multilingualism at the individual level is an enrichment. That's not the point of Bill 101."
Lisee said the point is ensuring that the next generation, and the one after that, will see a francophone society thriving in Quebec.
He called the latest census worrisome.
Statistics Canada reported Wednesday that 78.9 per cent of Quebec's population claimed French as their mother tongue in 2011, down from 79.6 per cent in 2006.
But that decline is largely due to immigration — and immigrants in Quebec are overwhelmingly learning French.
A newspaper columnist in Montreal La Presse used her own story to mock the limitations of the census data. She pointed out that while she lives in French, as a baby she grew up with Arabic lullabies so, according to the census data, she represents the demographic decline of French.
"Am I an allophone? A francophone? A telephone? There are days, frankly, when it all gets confusing," Rima Elkouri wrote in a column Thursday titled: Confessions Of An In-The-Closet Allophone.
"Today I don't speak, or sing, Arabic well enough to share (the same) lullabies with my children... Even if I'm an in-the-closet allophone, my life is essentially lived in French. These kinds of considerations, which reflect the pluralistic reality of a growing number of Montrealers, don't fit into any (census) category."
A number of Quebec politicians expressed alarm about the census findings.
The proportion of Quebecers who mainly speak French at home dipped slightly, to 81.2 per cent, from 81.8 per cent. In Montreal, 56.5 per cent of residents speak only French at home, 9.9 per cent just talk English and seven per cent speak only another language than English or French.
On the island of Montreal, Statistics Canada said the proportion of people who speak French at home has gone from 62.4 per cent in 2001 to 56.5 per cent in 2011.
"We see with these last Statistics Canada figures that the proportion of francophones in Montreal is declining, declining, declining. (Trudeau) says that's not a problem," Lisee said.
"So I'm asking to him, and others who don't see a problem, when will it become a problem: when we're 40 per cent? Thirty per cent? Twenty per cent?...
"We have, as elected officials in Quebec, and that means Justin Trudeau as well, we have a duty to make sure that this extraordinary experiment of a francophone society in North America endures."
Trudeau, a Montreal-area MP, made his remarks during a swing through Quebec City to promote his candidacy.
He arrived as a new CROP poll published by La Presse indicated he could lead the Liberals to a major rebound in Quebec and pass the NDP in popular support.
A Justin Trudeau-led federal Liberal party got the support of 36 per cent of the 1,000 respondents between Oct. 17 to 22 — a score not seen by Liberals in Quebec in years.
The NDP, which now holds most of Quebec's seats, clocks in at 30 percentage points, followed by the Bloc Quebecois at 19 percentage points, the Conservatives at 11 and the Greens at three per cent.
Trudeau downplayed the poll, saying there would be many more surveys until next year's leadership vote and until the next federal election around 2015.
In the next breath, however, he suggested the result is encouraging.
"This is an indication that Quebecers are open to a new kind of politics — one that engages, that listens," Trudeau said.
He added that he was determined to maintain one discourse across the country, and not tailor different messages to different regions. He suggested the NDP might be doing just that, with a nationalist message inside Quebec and a different one outside the province.
Trudeau did offer one nod to Quebec nationalists, by expressing support for the old Bill 101 that is the backbone of the province's current language policies.
The law, which has been watered down somewhat by court decisions and revised over the years, forbids immigrants and francophone children from attending English public schools; it also sets limits on the use of English on commercial signs.
Trudeau's support for the existing law stands in contrast with his father's position. The late prime minister criticized the original 1977 law and was a staunch opponent of Quebec nationalism.
"Let me say very clearly that I support Bill 101," Trudeau said Thursday.
"It is a reality that helps Quebec remain mainly French in a bilingual country. If we want Canada to remain bilingual — and I want it — we need to understand that Quebec must remain primarily francophone."
-With files by Alexander Panetta
Also on HuffPost