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.