By Thomas Buch-Anderson
Hans Christian Andersen's fairy tales and Soeren Kierkegaard's philosophical tomes were written in Danish.
So was the hugely successful 1993 novel by Peter Hoeg, Miss Smilla's Feeling for Snow.
But more and more Danes now use English at work, and when they buy books.
"One in six of every book sold in this country is in English. It's worrying because it undermines the Danish language," said Ib Tune Olsen, director of the Danish Publishers' Association.
"Soon it will not any longer be profitable to publish books in Danish," he added.
Hans Christian Andersen wrote in Danish
Globalisation has meant that Danish companies spend more and more time talking to people abroad - in English of course.
In recent years, some have even introduced English as the company language. Others advertise their Danish products to the Danish market in English.
In the education system too, an increasing number of schools teach in English and most scientific articles based on research from Denmark are published in English.
The Danish Language Council warns that the internationalisation of Denmark could come at a high price.
"Language is not merely an instrument of communication. Language is also culture and history," said Niels Davidsen-Nielsen, the council's chairman.
The cultural and historical loss would be awful - it's comparable to a natural environment where all the species have died out.
Danish Language Council
"We have had a written Danish language for the last 1,000 years, we have our literature, we grew up with Danish, we made all our experiences with Danish.
"If you imagined a scenario where there was only one language in the world, the cultural and historical loss would be awful. It's comparable to a natural environment where all the species have died out."
Danish, which is an official EU language, is spoken by five million Danes of whom most live in Denmark.
But according to the council, it could disappear as a complete language in 20 or 30 years if nothing is done to protect it.
"You use it or you lose it," said Niels Davidsen-Nielsen who is also part of a working group under the Danish Ministry of Culture, which is preparing the first national law to safeguard Danish.
Lately, stars on the Danish rap music scene have joined the fight to keep their language alive.
My own language is like a big sea where I can dive - I know it in and out, and I can tweak it so much better than English
The best-selling rap group, Malk de Kojn, insists on writing, rhyming and rapping in its mother tongue.
"With Danish, I have a full vocabulary. My own language is like a big sea where I can dive. I know it in and out, and I can tweak it so much better than English", says Anders Tuxen, the group's lead singer.
But even young children are now reading in English - untranslated Harry Potter books, for example, are very popular.
"English books are cheaper and the language so much richer in words," said Claus Boldrup, Manager of the GADs Boeger bookshop at the Illum shopping centre in Copenhagen.
Nina Havmund, 59, who has taken up learning English at courses in the city says she simply cannot get by without English:
"English is the common language in the world. You have to speak it to get by. Otherwise, you can't communicate with anyone - you can't even get a job."
Thomas Buch-Andersen reported for the Europe Today programme, on the BBC World Service.