In the recent past, not speaking Paraguay’s native language was no barrier to those seeking to gain or stay in power. When he was dictator, Stroessner never made a single address in Guaraní (although his wife spoke the language and he rewarded rural Guaraní-speakers with land for their loyalty to his regime).

But now, voters are encouraged to check if candidates speak the language, and those who do not face mockery on social media. The most recent politician to feel the repercussions was Santiago Peña, a close ally of President Horacio Cartes.

In a result that surprised many, Mr. Peña failed to secure his party’s nomination to contest the presidential elections in 2018, losing last month in the primary of the ruling Colorado party to Mario Abdo. One of the reasons for Mr. Peña’s downfall was an elitist image painted by his opponents, aided in no small part by his inability to speak Guaraní — something Mr. Abdo did not hesitate to point out during the campaign.

Under pressure from the electorate, Mr. Peña took a crash course in the language, but it appeared to have done little to sway voters.

“It wasn’t like this before,” said Maria Gloria Pereira, a policy maker and former head of curriculum at the Ministry of Education. “Politicians feel this pressure, because they know now that those that don’t speak the language of the people are far from the people.”