ASUNCIÓN, Paraguay — Legislators on the floor of Congress deliver speeches in it. Lovers entwined on Asunción’s park benches murmur sweet nothings with its high-pitched, nasal and guttural sounds. Soccer fans use it when insulting referees.
To this day, Paraguay remains the only country in the Americas where a majority of the population speaks one indigenous language: Guaraní. It is enshrined in the Constitution, officially giving it equal footing with the language of European conquest, Spanish. And in the streets, it is a source of national pride.
“Only 54 of nearly 12,000 schools teach Portuguese,” said Nancy Benítez, director of curriculum at the Ministry of Education, of the language of Brazil, the giant neighbor that dominates trade with Paraguay. “But every one of our schools teaches Guaraní.”
Paraguay differs significantly even from other multilingual Latin American nations like neighboring Bolivia, where a majority of the population is indigenous. Languages like Quechua and Aymara are spoken by different groups there, but rarely by people of mixed ancestry or the traditional elite.
In Paraguay, indigenous peoples account for less than 5 percent of the population. Yet Guaraní is spoken by an estimated 90 percent of Paraguayans, including many in the middle class, upper-crust presidential candidates, and even newer arrivals.
“Mba’éichapa?” asked Alex Jun, 27, a Korean immigrant who works in his family’s restaurant in Asunción’s old center, as he greeted customers with a Guaraní phrase translating as “How are you?”
“We’d go broke if we didn’t know the basics,” he explained.
Linguists and historians say the complex reasons for the broad use of the indigenous language here date to the earliest days of Spain’s incursions in the 16th century. The encomienda, a system common within the Spanish empire that forced indigenous people to work for Europeans and their descendants, did not penetrate big parts of the territory that eventually became Paraguay.
Meanwhile, Jesuits created communities for the Guaraní and other indigenous groups covering vast expanses, as depicted in the 1986 film “The Mission.” They armed Guaraní Indians against slaving expeditions, while nourishing the language in books and sermons.
When Spain expelled the Jesuits in 1767, more than 100,000 Guaraní speakers spread throughout Paraguay, said Shaw N. Gynan, an American linguist. Decades later, Guaraní speakers formed the bulk of support for the post-independence ruler José Gaspar Rodríguez de Francia, who took aim at the Spanish-speaking elite.
A despot who ruled until 1840, Francia was called Caraí Guazú, Great Lord. He banned those in the light-skinned upper class from marrying each other, sealed Paraguay’s borders and used Guaraní-speaking informants called pyragues, or fleet-footed ones, to bolster his tyrannical regime.
The result: a hobbled Europeanized elite by the end of Francia’s rule. Other dictators would later use Guaraní to stir nationalist fervor. Generals rallied troops in Guaraní in the devastating Triple Alliance War in the 1860s, which killed more than 60 percent of the population.
Isolation also sustained Guaraní. The Paraguayan novelist Augusto Roa Bastos, who mixed Guaraní with Spanish in his writing, called this landlocked, California-size nation an “island surrounded by land.”
Under Gen. Alfredo Stroessner, the dictator who ruled from 1954 to 1989, Guaraní thrived. At one point during General Stroessner’s rule, the writer Graham Greene warned that visitors risked being shot in the street by police officers if they did not understand Guaraní.
General Stroessner, the son of a Bavarian immigrant and his Guaraní-speaking wife, made it an official language, employed his own espionage network of pyragues and rewarded rural Guaraní-speakers with land for their loyalty.
“As disturbing as this may seem, political leaders in Paraguay have found it convenient to appeal to the masses in Guaraní, often suppressing liberalizing forces in the process,” said Mr. Gynan, the linguist.
When democratic rule was established in the 1990s, steps again were taken to strengthen Guaraní. The 1992 Constitution made Guaraní equal to Spanish. Officials said they have aggressively expanded Guaraní instruction in primary schools.
Teaching Guaraní is a subject infused with nationalism and competing theories of how to prevent Guaraní from being eclipsed by Spanish, long dominant in the legal system and in business.
Meanwhile, Guaraní is treading into new realms. Works like “Don Quixote” and the “Book of Mormon” recently gained Guaraní translations. Those proficient in written Guaraní exchange text-messages farewells like “Jajuecháta Ko’érõ,” which means, “We’ll see each other if tomorrow comes.”
A vibrant linguistic crossroads also persists in yopará, a mixture of Guaraní and Spanish. One yopará phrase is “ley del mbarate,” or “law of the strongest.” It captures the essence of a nation known as a haven for smugglers, arms dealers and counterfeiters.
Guaraní has also made diplomatic inroads. The former American ambassador, James Cason, a fluent Guaraní speaker who described it as “probably harder than Chinese,” recorded a Guaraní folk-song album in 2008 that put him on some radio stations’ playlists.
“It was obviously astute for Cason to do this,” said María Eva Mansfeld de Agüero, a member of the National Bilingualism Commission. “A diplomat here shouldn’t just speak Spanish at cocktail parties.”
Not everyone is bullish about Guaraní’s prospects. Ramón Silva, a poet and essayist who hosts a daily television program in Guaraní, is one skeptic. “Guaraní is slowly advancing to its death,” he said.
“It’s the perfect language for verbally disemboweling an adversary,” Mr. Silva said. “But Guaraní is in intensive care.”
He said his major concern involved the creation of new words in Guaraní to replace words borrowed from Spanish. “Using poorly created words may be well intentioned,” he said, “but neglects the reality of the language and pushes speakers into Spanish.”
Mr. Silva’s books still sell out, including a poetry collection titled “Na’ápe,” a work he proudly called “anti-dictatorial and vulgar.” The title, which translates as “take this” or “showing the middle finger,” opens a window, he says, into Guaraní’s mischievous capacities.
Others here share Mr. Silva’s concerns about Guaraní’s long-term future, pointing to factors like the increasing migration of peasants from the rural interior, where Guaraní is often the dominant language, to cities, where Spanish holds more sway.
Still, for a glimpse into Guaraní’s future, and the nationalist sentiment the language still arouses among some speakers, the writing may literally be on Asunción’s walls.
As many Paraguayans chafe at Brazil’s rising economic profile, one line of graffiti scrawled here reads, “Itaipu Ñane Mbae.” It refers to the huge Itaipu hydroelectric dam on the border with Brazil, owned by both nations but viewed by some as a symbol of submission to South America’s powerhouse.
“Itaipu,” the graffiti reads in translation, “is ours.”