Francis I, in his first public speaking event as pope in 2013, has said that English is his most challenging language. (Peter Macdiarmid/Getty Images)

The man who would one day be pope sat alone in his room for hours. The shy Argentine had come to snowy Dublin in January 1980 to live in a bleak one-room apartment. On a sabbatical at the Milltown Institute of Theology and Philosophy, 43-year-old Jorge Mario Bergoglio would try, for the first time, to learn English.

The school gave him a tutor.

According to one account, he went to the bursar’s office to ask for £14 pounds to buy language tapes.

By the time the name Jorge Bergoglio meant something to the world, those who were with him at the Jesuit university couldn’t remember much when reporters came asking. Just that he kept to himself, alone in his room.

Praying, most likely. Practicing, most certainly.

Jorge Mario Bergoglio, seen here as a young priest in 1973, studied English in Dublin in 1980. (Courtesy of Sergio Rubin/Clarin/via AFP/Getty Images)

“The hardest [language] for me has always been English. Above all, the pronunciation, because I don’t have an ear for it,” Pope Francis would later tell a biographer.

After three months of studying in Ireland, he never caught on to English — the language he will encounter when he sets foot in the United States for the first time Tuesday.

Until now, it has never been much of an issue: As a modest cleric, he spent his life in Argentina. He dedicated his time to Spanish-speaking parishioners. He could speak Italian, some German and some French, but as he rose through the church ranks, Bergoglio had no interest in being what he calls an “airport bishop.”

“When he became archbishop of Buenos Aires, apart from annual visits to Rome, I’m only aware of three trips he ever made,” said biographer Austen Ivereigh. “He was one of the least-traveled archbishops in the world.”

Before Bergoglio traveled to Italy for the 2013 papal election, he had reserved a room in a retirement home for his twilight years. There, he planned to live out his days serving the Catholic Church, speaking Spanish as usual.

Then Bergoglio found out his plan was changing. Shocking the Catholic world, an unpretentious South American priest became the man whose every word, in any language, matters to 1.2 billion people.

Pope Francis recorded a short video welcoming all those planning to trek to Philadelphia in order to see him. (World Meeting of Families)

The pope’s fans and followers in the United States hope he can deliver a message to President Obama, Congress, the United Nations and the American people that can expand the image of the Catholic Church beyond divisive issues such as abortion and gay marriage and toward shared values of open arms and caring for the disadvantaged.

So it’s back to the English tapes or tutoring, or however a 78-year-old world leader crams for big events in a language not his own.

“He’s been practicing for months now,” said Helen Osman, a key planner of the pope’s visit for the U.S. Conference of Catholic Bishops. “It’s very important to him that he clearly communicates what he’s trying to say.”

So far, clear communication has been a bit of a problem for the pope. Known for going off on unexpected tangents, his comments reverberate through churches and news cycles around the world.

The Spanish he speaks is Argentine Spanish, a unique dialect. More than an accent, it’s a distinct way of forming sentences and choosing words.

A Spanish speaker from North America expressing the concept “You have . . .” might begin the sentence with “Tú tienes . . .” Someone from Argentina would say “Vos tenés . . .” Nothing that would be hard for another Spanish speaker to understand.

But “there are words Argentinians use that could be considered bad words, strong words, in the rest of Latin America,” explained Alejandro Bermúdez, director of the Catholic News Agency and ACI-Prensa, the largest Spanish Catholic news organization.

Last year in Rio de Janeiro, Francis encouraged young people not to “stand on the balcony of life.” He told them to “Hagan lío.”

“ ‘Lío’ is a word used all across South America,” Bermúdez said. “In Argentina, [the phrase] would be translated, ‘Go and be heard’ or ‘Make yourselves heard loudly.’ In Mexico, for example, it would sound like, ‘Go get into trouble’ or ‘Go make a mess.’ ”

This phrase has become a motto among Spanish-speaking youth. Search “Hagan lío” online, and you will find it scrawled across posters and drawings of the pope. It’s even inspired memes: “Keep Calm and Hagan Lío.” This upset some adults. Francis seemed to find it funny, joking later in Paraguay that youth should hagan lío — but remember to clean up their lío.

“He’s very much aware, but he’s not intimidated of using his Argentinian way to speak,” Bermúdez said. “When he goes off the cuff during his U.S. visit, I really pray that he will have a translator that is familiar with Argentinian Spanish.”

Rest assured, he will. Although Francis travels with a personal interpreter, the Conference of Catholic Bishops hired CSI Conference Systems to manage more than a dozen intrepreters for the trip. When the pope speaks at large events such as the Mass at the Basilica of the National Shrine of the Immaculate Conception on Wednesday, real-time translations will appear on large screens. In some smaller settings, participants will be able to hear an interpreter through individual headsets. TV audiences will hear real-time interpretation or see captioning.

Francis is expected to speak English in delivering four of his 18 speeches in Washington, New York and Philadelphia, including at the United Nations, the White House and Congress — the places where his remarks will be most closely watched. Yet even there, he may need some interpreting services.

“I think we’ll see that he has the ability to connect with people at a deep, emotional level. He reaches people in the heart,” said John Gehring, author of “The Francis Effect.” “But it seems when he wants to communicate from the heart, his most passionate pleas are in Spanish.”

The pontiff is expected to discuss inequality, climate change, political divisiveness, religious liberty and immigration — topics that some say are likely to get heated.

Although today’s Americans are accustomed to an English-centered world, it wasn’t until modern times that a pope had any interest in speaking the language. Most pontiffs associated with the Italian tongue and a strict dedication to Latin; more than 250 popes reigned before the Catholic Church would allow for Mass to be said in another language. And the only English-born pontiff, Adrian IV (1154-1159), grew up in France.

Pope John Paul II changed the game. As he traveled to an unprecedented number of countries, he learned to speak the languages of the people to the people.

“He recognized that in order to be an effective actor on the international stage, he had to use vernacular languages as best he could in the countries he went to,” said Ken Pennington, a history professor at Catholic University.

Charismatic in his own right, Francis realizes the same, Pennington said. Although some worried about his language skills when he chose to speak only in Italian during Vatican papal audiences, he has been slowly building his skills. After debuting his English in a prerecorded video, he has made comments in English in South Korea, the Philippines and on an ABC program previewing his trip to the States.

Francis’s dialect is heavily accented but fairly clear. He seems to have the most trouble pronouncing consonants: A word such as “war” sounds like “or,” and “like” sounds like “lie.”

“How many times do leaders from the United States go to other countries and speak in English? You don’t have to speak every language possible to be a world leader,” said Hosffman Ospino, a Hispanic ministry professor at Boston College.

The decision to speak Spanish, Ospino noted, is not just a matter of personal convenience. Hispanic Catholics account for 71 percent of the church’s growth since 1960, according to his research. The choice is widely perceived as a nod to the importance of that community.

When he speaks in Spanish, much of the church in this country will understand him perfectly, Ospino said. No interpreter, subtitles or language tapes needed.