I was assigned to read this short story in a college science fiction course around 2000. All I remember is that the plot involved a book(?) or a series of writings about an ancient or possible alternate-universe culture, that people became obsessed with, to the point where they began adopting the customs, language, etc. of this alien culture--until, gradually, it's as if Earth has been replaced by that culture, and that other world is effectively brought into existence. No idea of title, author, or year it was written.
"Tlön, Uqbar, Orbis Tertius" is a short story by the 20th-century Argentinian writer Jorge Luis Borges. The story was first published in Spanish in Argentina in May 1940. The first English-language translation of the story was published in 1961.
The synopsis of the story is as follows:
In a fictional timeline of 1940 Borges and his friend and collaborator, Adolfo Bioy Casares, find a encyclopedia which is an American clone of the 1902 edition of Encyclopædia Britannica with mysterious discrepancies between their reprints.
In one of those reprints there are allusions to a mysterious country called Uqbar situated in a world called Tlön. These allusions do not appear in any other reprint or in any other encyclopedia.
Later, Borges comes in possession of a volume of an English-language encyclopedia entirely devoted to Tlön. The people of the imaginary Tlön hold an extreme form of Berkeley's subjective idealism, denying the reality of the world.
By 1941, the world and the narrator have learned, through the emergence of a letter, that a "benevolent secret society" was formed in the 17th century. Its main purpose was to create a country: Uqbar.
The American "eccentric" millionaire Ezra Buckley, one of the members of the restored sect, finds (in the late 19th Century) its undertaking too modest, proposing that their creation be of an entire world instead of just a country. He also adds that an entire encyclopedia about this world—named Tlön—must be written.
By 1942, Tlönian objects began to inexplicably appear in the real world.
By 1944, all forty volumes of the First Encyclopedia of Tlön have been discovered and published in a library in Memphis. The material becomes accessible worldwide and immensely influential on Earth's culture, science and languages. By the time Borges concludes the story, presumably in 1947, the world is gradually becoming Tlön.