When he was 17, Higgs "had this kind of crazy teenage idea." He had begun using Duolingo, a mobile language-learning app, to study French, and wondered if the creators had considered adding support for Irish.

"I didn't get a reply," Higgs said.

Invention and reinvention

Duolingo is based on the idea that if learning is gamified and bite-sized (and free), people will stick with it when they might not otherwise. Users of its smartphone or web app are presented with short, five minute lessons in which they identify words, translate short sentences, or practice speaking and listening. Users earn points for passing lessons, and they can compete in daily and weekly leaderboards.

Duolingo's roots are in spam — or, rather, the fight against it. Co-founder Luis von Ahn made his fortune selling reCaptcha, the irritating but necessary software which makes you prove "I'm not a robot" when filling out certain forms online.

Von Ahn founded Duolingo while teaching at Carnegie Mellon University, alongside his graduate student Severin Hacker. Both were non-native English speakers working in the United States — von Ahn was born in Guatemala, Hacker in Switzerland — and they had seen how access to language learning had improved their earning potential. They wanted to create a free language app that would make money by providing translation services for other websites.

"(Von Ahn's) field of research has always been in human-computer interaction," said Duolingo spokesman Sam Dalsimer, who met with CNN Business at the company's Pittsburgh headquarters.

Dalsimer described the app's original concept as one that would allow people to learn languages while simultaneously translating the internet. The translation part of the business model worked for a bit before the founders realized that artificial intelligence was quickly supplanting their human translators as the cheapest option.

Duolingo's lofty mantra fits right alongside the most ambitious in Silicon Valley: "Making language education free, fun and accessible for everyone in the world." But the company initially focused on the most profitable languages that had the biggest potential reach and userbase. It generated income by selling display ads against the courses and premium subscriptions, and by forging various partnerships.

Higgs' email arrived at the perfect time, when some in the company were questioning the focus on major languages like English and Spanish, and wondering whether they could expand the program to include smaller tongues.

Nor was Higgs the only person to email Duolingo asking the company to add a particular language, or to castigate the developers for choosing one language over another. The team was inundated with offers to volunteer to build courses for new languages, if they would only provide a way.

"People really wanted to contribute to get their language into the Duolingo system," community specialist Myra Awodey told CNN Business. Awodey works with language communities educators to develop new courses.

"That's kind of how the incubator came about."

"But we had this heartfelt plea from I think a high schooler at the time," Awodey said. "(Our founder) was like, why not? This guy sounds cool. He's serious, let's just do it."

Irish became the first endangered or minority language added to the platform, though Higgs would not join the team for another year or so.

"Its been a massive, massive benefit to the language," said Oisín Ó Doinn, a learning technologist at Dublin City University and one of the original creators of the Duolingo Irish course. "It contributes to the ecology, the learning ecology around the language."

He said that many language learners in schools had begun using the app to supplement their studies, and that it has been a huge success in the United States thanks to pickup from the Irish diaspora.

New approach to endangered languages

The success of the Irish course has cultivated a mini revolution inside Duolingo, which now employs 190 designers, developers, linguists, computer scientists and other staff in Pittsburgh.

"We had to focus in the beginning on the courses that had the most demand and largest audience served," said product manager Conor Walsh. "But the cool thing about technology is that the incremental cost decreases. Now that we have all these courses, and we've ironed out a lot of the technical complexity, now adding a new course, in many ways, doesn't cost us that much."

Access to minority language learning also has the ability to empower communities, he said.

Awodey, the Duolingo community specialist, agreed.

"I do feel like we have a responsibility as a company promoting these majority languages, and contributing to some of the trends that are further marginalizing minority languages," to do something about it, she said.

"It's really important that people see a language like Welsh as something they can interact with and use on modern devices," said Jonathan Perry, a language teacher who works on Duolingo's Welsh course. "It brings the language up to date with modern technology usage which is absolutely so essential that a language feels fresh and used."

Since Irish's rollout in 2013, Duolingo has added Welsh, Hawaiian and Navajo, along with the constructed global language Esperanto. Haitian Creole, Scottish Gaelic, Latin and Yiddish are currently in the incubation stage.

There's also a business justification. The more languages Duolingo adds, the more potential users are exposed to the app (and its advertisements). Minority and heritage language communities are also a user base where there is less competition from other services, as opposed to the multitude of apps which claim to help you learn French or Spanish.

"Irish was the test case because we were the first minority language on the platform and we're still one of the most popular courses," said Ó Doinn. (Irish is among the top 50% of courses as measured by active learners, and the most popular minority language.)

Political red lines

Of course, there's a big difference between picking up a few words in Irish or Welsh to make you feel as if you're connecting with your ancestors, and actually learning a language — particularly an endangered one that needs all the speakers it can get.

"Who's the audience for the Hawaiian course? Is it going to be tourists? Mostly? Because that would affect the content," said Awodey. "Or is it going to be primarily built by and for indigenous speakers and people reconnecting with the language?"

Despite this, however, the Duolingo Hawaiian course can sometimes risk speaking down to native Hawaiians, few of whom need teaching, for example, what a "lei" is.

"Everyone was super excited about it, but it's totally tapered off because it's not for natives, it's too baby, it's too simple," said Kū Kahakalau, executive director of Hawaiian language and culture NGO Kū-A-Kanaka.

Linguistic politics are often fraught with regard to majority tongues, let alone for endangered languages that have a long history of colonialism and disrespect. Scrutiny of such courses is always going to be tighter, and invisible red lines easier to cross.

"When you're dealing with a heritage language, it does come with a bundle of stuff that we don't have when teaching English," said Duolingo learning scientist Hope Wilson. "There are lots of tricky issues to get into, very often there are divides within the communities where people don't agree on, you know, issues of spelling or that kind of thing."

Visibility and viability

The question of effectiveness is particularly fraught when it comes to endangered or minority languages. But even if Duolingo isn't minting millions of new Hawaiian speakers, there are other ways in which the presence of a language on the app can help.

Visibility and prestige are vitally important to preserving and promoting endangered languages. Minority and endangered languages are generally at risk because they are marginalized within their own countries or communities. Anything that can improve their standing can go a long way to helping preserve them.

"Even if people aren't becoming entirely fluent with the app, it's hugely beneficial in terms of raising visibility and that's incredibly important," said Ó Doinn, the Irish course creator. "Status and support are the most important things for facilitating a language's usage."

Ó Doinn, Perry, Higgs and Kahakalau all pointed to the ability to have their phone's interface in their native language as a key factor in this regard.

"My phone is in Irish because I have an Android and I'm able to make that decision," Ó Doinn said. "My Gmail is in Irish. These things are done for free by the community for the community. If we open up those resources that people can modify themselves, that's really important for preserving minority languages online."