Before he could board a recent Ryanair flight to London, Dinesh Joseph, a 45-year-old South African leadership and management trainer, had to pass a test about South Africa to prove his nationality.

The test was in Afrikaans, a language once imposed by the former white-led apartheid government and one that many South Africans do not even speak today. When Mr. Joseph asked to take the test in English, he said, a Ryanair customer service agent told him: “No, this is your language.”

Mr. Joseph, who is of Indian descent and grew up in South Africa speaking English, said he thought he was the target of a prank. “What on earth is this?” he asked himself.

But Ryanair now requires South African passport holders traveling to the United Kingdom to fill out what the company described in a statement as “a simple questionnaire” in Afrikaans. Those unable to complete the questionnaire are not allowed to travel and are issued a refund, the airline said in the statement.

The U.K. high commission in Pretoria, which heads Britain’s diplomatic mission in South Africa, said on Twitter that the test was not a U.K. government requirement.

In social media postings, South Africans have accused Ryanair of racism and ignorance for failing to grasp the historical connotations of the language. During the height of the struggle against white minority rule, Afrikaans was a crucial point of tension.

In its statement, the company, a low-cost airline based in Dublin, cited a “high prevalence of fraudulent South African passports” and did not respond to questions about its choice of Afrikaans or when it implemented the policy.

South Africa has more than 10 national languages today, but Zulu is the most widely spoken household language, with 23 percent using it. Afrikaans is third at 13 percent. (Second is Xhosa at 16 percent. English is the household language of 8 percent of South Africans.)

South African officials were disturbed by the move. “We are taken aback by the decision of this airline,” Siya Qoza, a spokesman for South Africa’s Minister of Home Affairs, said in a statement.

South Africa has recently made public some cases of passport fraud, and Mr. Qoza said the government was working to put an end to this abuse. It has also given airlines access to systems that allow them to screen travelers and authenticate South African passports, he said.

“It is not clear to which extent the airline has used these services before resorting to this backward profiling system,” Mr. Qoza said.

The questions on the airline’s nationality questionnaire, which has been seen by The New York Times, asked travelers the name of the president of South Africa, the country’s phone code, and its national animal, flower and colors. “Name three of South Africa’s official languages,” one question reads.

With the help of Google translate, Mr. Joseph, the South African leadership trainer, managed to fill out the form and board the plane from the Spanish island of Lanzarote.

“But the indignity of them pulling out a marking sheet, I just felt so small. I felt embarrassed,” he said. “They’ve taken no effort to understand South Africa as a nation.”

Sihawukele Ngubane, a professor of linguistics at the University of KwaZulu-Natal, in South Africa, said that Afrikaans originated with Dutch colonizers who arrived in the 17th century.

In the 20th century, he said, the Afrikaans-speaking National Party government, which enforced apartheid, turned it into an official language, alongside English, and imposed it over nine Indigenous languages that were spoken by the majority in South Africa.

Assessing South Africans by their knowledge of Afrikaans is unfair, Mr. Ngubane said, adding that a minority of South Africans speak it even as a second language. He said many still perceive it as the language of the oppressor. “That connotation still exists.”

Word of Ryanair’s policy has emerged just ahead of the June 16 national holiday in South Africa that commemorates the 1976 Soweto uprisings. About 20,000 Black schoolchildren marched that year to protest the government’s effort to require all instruction to be done in Afrikaans. They were met with deadly force by the police.

“How in 2022 are we having the same fights?” asked Petronia Reddy, a 36-year-old South African who missed her Ryanair flight from London to Dublin on June 1 because she was told she had “failed” her test in Afrikaans. (In its statement, Ryanair said the questionnaire was for those traveling to the U.K.)

“You can’t tell a nation that has been through what it’s been through and a brown person from South Africa that this form makes you South African,” Ms. Reddy, who is of Indian descent, said in an interview. She made her documents available to the The Times for review.

After she explained to staff members that South Africa has many official languages other than Afrikaans, the company ultimately put her on the next flight, she said, but the humiliation stuck with her.

“You start thinking about every other time you’ve been discriminated against,” she said. “It just is so triggering.”

John Eligon and Lynsey Chutel contributed reporting.