“A language is a culture,” she said. “In Belgium the two cultures know very little about each other because they speak different languages. There are singers known in one part, not in the other. Television is different, newspapers, books.”

Francophones have now come to talk about “linguistic cleansing.” Flemish, many of them openly resentful of subsidizing poorer French-speaking compatriots, who for years lorded it over them economically and otherwise (unemployment today is three times higher in rust-belt Wallonia), say the issue is preserving national heritage. “It’s difficult to have a rational conversation,” said Roel Jacobs, a writer born to Flemish parents who lives in bilingual Brussels.

“There are six million Dutch speakers and they’re angry about Francophone influence, but meanwhile they care nothing about the influence of English and Anglo culture,” he went on, “so it’s not rational. We’ve forgotten our true cultural history. In the 15th century Bruges was the most vibrant city outside Italy because it was full of foreigners. Then it was Antwerp, when the foreigners left Bruges. Today the national movement in Flanders is in complete denial of the past.”

A century or so ago Émile Verhaeren, the Flemish Symbolist poet, who was born in Sint-Amands, near Antwerp, and educated at the University of Leuven, wrote in French. Now the university has split into two, the one Flemish, the other French and moved to Wallonia, and the region around Sint-Amands is a stronghold of far-right, anti-immigrant Flemish nationalists.

“Back then the Francophones didn’t want a bilingual country,” Ms. Witte said. “French dominated, and it would have meant they would need to learn Flemish. Educated Flemish spoke in French. But then the electoral system changed and allowed everyone to vote, and more power went to the non-French-speaking Flemish middle and lower classes.”

The other afternoon Francis Dannemark was at home in Brussels. Through the open French doors in his library, a Ping-Pong table crammed the balcony, beyond the stacks of books and DVDs. “I don’t think it will, but for the first time I really believe Belgium could disappear,” he said. Mr. Dannemark is an editor at Le Castor Astral, a French-language publisher. He prints translations of Flemish writers from Dutch, a rarity here.