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Media captionLanguage app Babbel got a big boost when the makers of hit TV show Narcos suggested a tie-up.

Eleven years ago, one of Thomas Holl's closest friends, Lorenz Heine, wanted to learn Spanish.

Thomas confidently assured him that there must be several easily accessible online courses to assist him in this quest. But when Thomas turned to Google, the then 32-year-old software engineer was surprised by the sparse results.

"I started a search and I couldn't find anything good," recalls Thomas, who at the time was working on a music-mixing programme for DJs.

"There were CD-ROMs, there were textbooks. But [at the time] not so much online."

A few months later, Thomas, Lorenz and two others decided to take matters into their own hands, and formed Babbel, a language learning website and app that now boasts one million paid members worldwide, and clocks up some 100,000 downloads a day.

But the journey from a loose concept scrawled on a wall of whiteboards in Berlin, to a global operation that works with the likes of computer giant Apple and video streaming service Netflix, was anything but straightforward.

Image copyright Babbel Image caption Babbel's website and app have one million paid users

"We were pretty arrogant," says Thomas of himself and his three co-founders. "We didn't know what we didn't know."

Not one of the company's young masterminds had any background in teaching languages, and at first they simply tried to adapt existing course materials.

"We did quite a lot of publishing deals where we would license content from publishing houses and try to put it online," says Thomas, who is now the company's chief strategy officer.

"But one thing we figured out in that process was that while the materials were good... we were having a very hard time.

"It would take us quite some effort to take those materials, and put them into a form that would work online, or that would work on a mobile phone."

Soon the team realised that they were better off starting from scratch, and creating their own bespoke courses.

Image copyright Marc Beckmann/Ostkreuz Image caption Thomas Holl admits that he and his co-founders didn't entirely know what they were doing when they first started up the business

Today Berlin-based Babbel is one of the most popular language learning apps on both Apple and Android devices.

But how exactly does it compete, in what is now a very crowded marketplace, with firms like Busuu, Duolingo, HelloTalk, Memrise, MosaLingua - and language learning veteran Rosetta Stone?

Thomas says that central to Babbel's success is that they realised from day one that there is not a "one-size-fits-all" approach to language learning.

Explaining what he means, he says that a Frenchman would find some elements of learning German easier than a Briton, because French and German both use grammatical gender - inanimate objects such as tables are given a male or female designation (and in German a neuter gender as well) .

Also, he says that a Spaniard should be able to gain fluency in Italian quicker than a Swede, because Spanish and Italian have a lot in common as Romance languages related to Latin.

With this theory in mind, Babbel's German course for English speakers is different to the German course for French speakers, and so on.

Image caption Babbel also teaches users about hand gestures and other nonverbal communication

The company also offers specific courses tailored for business people, or those going to a country on holiday.

Babbel's methods have won the company many fans, helping it to raise $22m (£17m) in a 2015 funding round.

It also came to the attention of tech giant Apple, for whom the German firm built a special version of its app for the launch of the Apple Watch. And it was approached by Netflix to make a Spanish learning tool to tie-in with the hit Spanish language TV show Narcos.

Annabella Da Encarnacao, Babbel's director of performance marketing, highlights another factor in the company's success.

Raised in Portugal and France, she was used to greeting people with kisses on both cheeks, but a pure language course, she says, wouldn't teach you that this is not standard practice in Germany.

So instead Babbel also works on supplementary nonverbal communication material that teaches just that, ranging from blog posts and discussion boards to short films made in its own small studio.

"The Italian gestures video is very popular," says Annabella, referring to a jovial five-minute tutorial that is one of the highlights of the company's active YouTube channel.

Image caption The language learning industry is crowded one

Babbel doesn't reveal its revenues, but the company makes its money from subscriptions. While users can access a basic service for free, they have to pay to unlock more content.

While Lorenz Heine has since left the company, Babbel is continuing to expand around the world. While most of its staff are based in Berlin, it realised a few years ago that it needed a permanent US presence if it wanted to crack that market.

In the US, Thomas says that such an on-the-ground approach is vital because it is so solidly English speaking, with just around one fifth of the population being bilingual, compared to more than 50% of Europeans.

"Within America, you don't actually have to speak another language," he says. "In general, you don't learn a language for job purposes."

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Instead, research showed, Americans were learning languages for aspirational reasons - to speak to a foreign-born girlfriend, or to learn a language spoken by an immigrant grandparent.

With this in mind, the company opened a New York office, and hired dozens of locals who better understood the needs of learners in the US.

Francine Espinoza Petersen, a professor of marketing at the European School of Management and Technology, agrees that Babbel is continuing to be successful because it tailors its services for different needs.

Image copyright Getty Images Image caption Babbel has also tried to help asylum seekers in Germany by helping them to download its app to improve their language skills

"Babbel is able to satisfy the basic need of communicating," she says. "But this is so different across people, across counties and across consumers - they were able, with technologies, to offer something localised and personalised at the same time."

But why the name Babbel? Thomas says it is a reference to the biblical story of the Tower of Babel and how God created a multitude of languages, and also the fact that "babbel" is a German word that means to talk in a friendly way.

Image caption English remains the language that most people are trying to learn

The next frontier for Babbel is apparently virtual reality, and the company envisions a future in which language learning will include interaction with another native speaker, albeit in pixel form.

However, despite its hi-tech plans, Thomas adds that the company's mission remains as simple as when it was founded: "Everyone should, and could, learn a language."