Duolingo Explained

Duolingo, Inc.
Company Type:Public
Location:Pittsburgh, Pennsylvania, U.S.
Area Served:Worldwide
Key People:Luis von Ahn (CEO)
Severin Hacker (CTO)
Industry:Online education
Products:
  • Duolingo
  • Duolingo ABC
  • Duolingo English Test
Services:Language, music, and mathematics courses and language assessment.
Revenue: (2023)
Operating Income: (2023)
Net Income: (2023)
Assets: (2023)
Equity: (2023)
Employees:≈ 720 (December 2023)
International:yes
Advertising:Yes
Registration:Yes
Users:103 million MAU (Q2 2024)
Launched: (private beta)
(public release)
Current Status:Online
Native Clients:Android, iOS, iPadOS
Footnotes:[1] [2] [3] [4]

Duolingo, Inc. is an American educational technology company that produces learning apps and provides language certification. Duolingo offers courses on music,[5] math,[6] and 43 languages, ranging from English, French, and Spanish to less commonly studied languages such as Welsh, Irish, and Navajo.[7] The learning method incorporates gamification to motivate users with points and rewards and interactive lessons featuring spaced repetition.[8] The app promotes short, daily lessons for consistent-phased practice.

Other services include the Duolingo English Test, an online language assessment, and Duolingo ABC, a literacy app for children. The company uses a freemium model with its optional premium services, Super Duolingo and Duolingo Max, being ad-free and offering more features.

With over 100 million monthly active users, Duolingo is the most popular language learning app.[9] [10] [11] A systematic review of research on Duolingo from 2012 to 2020 found comparatively few studies on the platform's efficiency for language learning but identified several studies that reported relatively high user satisfaction, enjoyment, and positive perceptions of the app's effectiveness.[12] The company has also been recognized for its successful marketing tactics and strong brand engagement.[13] [14]

History

Early history

The idea for Duolingo was formulated in 2009 by Carnegie Mellon University professor Luis von Ahn and his Swiss-born post-graduate student Severin Hacker.[15] [16] Von Ahn had sold his second company, reCAPTCHA, to Google and, with Hacker, wanted to work on an education-related project.[17] Von Ahn stated that he saw how expensive it was for people in his community in Guatemala to learn English. Hacker (co-founder and current CTO of Duolingo) believed that "free education will really change the world"[18] and wanted to provide an accessible means for doing so. He was recognized by the National Inventors Hall of Fame for his contributions to language learning and technological development.[19] The Duo mascot is a green owl because co-founder Severin Hacker hates the color green.[20]

The project was originally financed by von Ahn's MacArthur fellowship and a National Science Foundation grant.[21] [22] [23] The founders considered creating Duolingo as a nonprofit organization, but Von Ahn judged this model unsustainable. Its early revenue stream, a crowdsourced translation service, was replaced by a Duolingo English Test certification program, advertising, and subscription.[24] [25]

Funds

In October 2011, Duolingo announced that it had raised $3.3 million from a Series A round of funding, led by Union Square Ventures, with participation from author Tim Ferriss and actor Ashton Kutcher's investing firm A-Grade Investments.[26] Duolingo launched a private beta on November 27, 2011, and accumulated a waiting list of more than 300,000 people.[27] It launched to the general public on June 19, 2012, at which point the waiting list had grown to around 500,000.[28] [29]

In September 2012, Duolingo announced that it had raised a further $15 million from a Series B funding round led by New Enterprise Associates, with participation from Union Square Ventures.[30] In November 2012, Duolingo released an iPhone app,[31] followed by an Android app in May 2013, at which time Duolingo had around 3 million users.[32] By July 2013, it had grown to 5 million users and was rated the No. 1 free education app in the Google Play Store.[33]

In February 2014, Duolingo announced that it had raised $20 million from a Series C funding round led by Kleiner Caufield & Byers, with prior investors also participating.[34] At this time, it had 34 employees, and reported about 25 million registered users and 12.5 million active users; it later reported a figure closer to 60 million users.

In June 2015, it announced that it had raised $45 million from a Series D funding round led by Google Capital, bringing its total funding to $83.3 million. The round valued the company at around $470 million, with 100 million registered users globally.[35] In April 2016, it was reported that Duolingo had more than 18 million monthly users.[36] [37]

In July 2017, Duolingo announced that it had raised $25 million in a Series E funding round led by Drive Capital, bringing its total funding to $108.3 million. The round valued Duolingo at $700 million, and the company reported passing 200 million registered users, with 25 million active users.[38] It was reported that Duolingo had 95 employees.[39] Funds from the Series E round would be directed toward creating initiatives such as a related educational flashcard app, TinyCards, and testbeds for initiatives related to reading and listening comprehension.[40] On August 1, 2018, Duolingo surpassed 300 million registered users.[41]

In December 2019, it was announced that Duolingo raised $30 million in a Series F funding round from Alphabet's investment company, CapitalG.[42] The round valued Duolingo at $1.5 billion. Duolingo reported 30 million active users at this time. The headcount at the company had increased to around two hundred, and new offices had been opened in Seattle, New York, and Beijing.[43] Duolingo planned to use the funds to develop new products and further expand its team in sectors like engineering, business development, design, curriculum and content creators, community outreach, and marketing.[44]

Features and media

In October 2013, Duolingo launched a crowdsourced language incubator.[45] In March 2021, it announced that it would be ending its volunteer contributor program and donating money to its volunteer contributors who helped develop it. The company said that from now on, language courses would be maintained and developed by professional linguists aligning with CEFR standards.[46] On June 28, 2021, Duolingo filed for an initial public offering on NASDAQ under the ticker DUOL.[47] From August 2021 to June 2022, the Duolingo language learning app was removed from some app stores in China.[48] In the early 2020s, Duolingo was noted for its viral videos on the social media platform TikTok.[49] [50]

In August 2022, Duolingo overhauled its interface, changing its course structure from a tree-like design, where users could choose from a range of lessons after completing previous ones, to a linear progression. This update has been criticized by users across social media outlets, such as Reddit and Twitter.[51] CEO Luis von Ahn stated that there were no plans to reverse the changes—intended to simplify Duolingo for its new users—maintaining both the old and new versions would be difficult.[52] In October 2022, Duolingo acquired Detroit-based animation studio Gunner; it is the studio that produces art assets and animation for Duolingo and Duolingo ABC and its marketing campaigns. In October 2023, Duolingo released math and music courses in English and Spanish for iOS users.[53]

In March 2023, Duolingo officially announced the planned Duolingo Max, a subscription tier above Super Duolingo, in their blog.[54] In July 2023, Duolingo launched a feature using the iOS widget feature. In January 2024, after having laid off around ten percent of its contractors, Duolingo began using artificial intelligence to replace tasks usually done by its contractors.[55] [56] In March 2024, the widget feature was also on Android.[57] In 2024, Duolingo acquired Detroit-based design studio Hobbes.[58]

Services

Duolingo

On Duolingo, learners learn by engaging with the language. Users complete lessons using words they are learning.[59] Duolingo uses a gamified approach to language learning, with lessons that incorporate translating, interactive exercises, quizzes, and stories.[60] It also uses an algorithm that adapts to each learner and can provide personalized feedback and recommendations. Lessons are designed to be brief, allowing users to learn in manageable chunks.[61] [62] Duolingo also provides a competitive space,[63] such as in Leagues, where people can compete against their friends or see how they compare with randomly selected worldwide player groupings of up to 30 users. Rankings in Leagues are determined by the amount of "XP" (experience points) earned in a week. Badges in Duolingo represent achievements earned from completing specific objectives.[64]

Duolingo provides features that allow teachers to track their students' progress.

Duolingo currently offers the following language courses:[65]

The app has a personalized bandit algorithm system (later the A/B tested variant recovering difference softmax algorithm) that determines the daily notification that will be sent out to the user.[66]

Duolingo has a widget feature on iOS and Android. The widget feature initially started as Duolingo's annual hackathon project. The iOS widget has 39 illustrations designed by Kyle Ruane that were intended to be another daily reminder to complete lessons. On the top part of the widgets is the user's daily streak. The company owns a blog called Duolingo Blog[67] that publishes self-data reports of the common language selected in the Duolingo app. On the Duolingo Blog, they wrote that they "decided to come up with a series of illustrations that would show Duo’s mood at different parts of the day". Any lesson completed in Duolingo will count towards the user's daily streak.[68] The daily streak's visual symbol in the app is fire.

Subscriptions

Super Duolingo

Most of Duolingo's language learning features are free, with periodic advertising in its mobile and web browser applications, which users can remove by paying a subscription fee or promoting referral links.[69] This program, known as Super Duolingo, includes benefits such as unlimited hearts (retries), level-skipping, no ads, and progress quizzes.[70]

Duolingo Max

Duolingo Max is a subscription above Super Duolingo that adds additional functions using generative AI: Role Play, an AI conversation partner, and Explain My Answer, which breaks down the rules with a modified GPT-4 when the user makes a mistake; users can also have video chat with one of the characters. Intended to provide further immersion through "free-flowing conversation",[71] it is available on the iOS version of the Duolingo app in selected courses and markets for English speakers.[72]

Duolingo ABC

Duolingo ABC is a free app designed for young children to learn letters, their sounds, phonics, and other early reading concepts. Released in 2020, it does not contain ads or in-app purchases. As of April 2024, iOS and Android versions are available, but only in English.[73] [74]

Duolingo Math

Duolingo Math is an app course for learning elementary mathematics. It was announced on YouTube on August 27, 2022, at the Duocon 2022 event.[75]

Duolingo Music

In March 2023, Duolingo was reportedly developing a new music course that would allow users to learn how to read and play music through its gamified learning experience.[76] [77] On October 11, 2023, Duolingo formally unveiled Duolingo Music in a YouTube Short,[78] a new platform within the existing app that provides basic music learning through piano, drums, and sheet music lessons. [79] [80], it is currently available on iOS and Android devices.[81] Since 2024 users can practice music by playing pop songs in the course.[82]

Duolingo English Test

See main article: Duolingo English Test.

The Duolingo English Test (DET) is an online English proficiency test that measures proficiency in reading, writing, speaking, and listening in English. It is a computer-based test scored on a scale of 10–160, with scores above 120 considered English proficiency. The test's questions algorithmically adjust to the test-takers' ability level. The test's certificate is reportedly accepted by over 5,000 programs internationally,[83] albeit with exceptions.[84]

Business model

Duolingo had revenue of $531 million in 2023, compared to $250.77 million in 2021.[85] Its revenue was $1 million in 2016, $13 million in 2017, and $36 million in 2018.[86] In May 2022, it was reported that 6.8% of its monthly active users paid for the ad-free version of the app.[87]

Duolingo derives most of its revenue from subscriptions, advertising, and its Duolingo English Test.[88] In April 2020, it passed one million paid subscribers;[89] it reached 2.9 million in March 2022,[90] and 4.8 million at the end of March 2023.[91]

Reception

Effectiveness

A 2017 study found no significant difference between elementary students learning Spanish through the "gamification" of the Duolingo app and those learning in classroom environments, with both groups demonstrating a similar increase in achievements and self-efficacy.[92]

Duolingo's occasional use of 'erratic' phrases—such as "The bride is a woman and the groom is a hedgehog" or "The man eats ice cream with mustard"[93] —is reportedly derived from research published in 2018 by psychologists at Ghent University in Belgium,[94] which concluded that such "semantically unpredictable sentences" were more effective for language learning than conventional and predictable phrases, based on the concept of "reward prediction errors", in which unexpected or surprising outcomes are more rewarding and thus encourage further learning.[95]

A 2022 study on adults using Duolingo as their only language learning tool, published in the journal Foreign Language Annals, found that participants who completed a course had similar reading and listening proficiency to university students after four semesters of study, concluding that Duolingo could be an effective tool for language learning.[96] Another 2022 study of Malaysian students learning French, published by the National University of Malaysia Press, found that the app facilitated the acquisition of vocabulary and concluded that it was "well suited" for beginners in this regard.[97]

According to Duolingo's own 2021 study, five sections of the app are roughly equivalent to five semesters of university instruction, and Duolingo is an "effective tool [...] at an intermediate level".[98] [99] A 2023 study funded by Duolingo concluded that Duolingo English learners did not significantly learn much grammar.[100] Duolingo English learners in Colombia and Spain were found to gain significantly more proficiency than students in a classroom, except for listening.[101]

Criticism

Some language professionals have criticized the app for its limitations and gamified design.[102] Others have pointed out that Duolingo and similar apps can be a starting point but lack the human interaction required to be fluent in a language and for real-life conversations.[103] Players have also reported that "gamification" has led to cheating, hacking, and incentivized game strategies that conflict with actual learning.[104] Duolingo's study conclusion has been criticized for being "a meaningless assertion."[105]

In March 2022, Duolingo forums were discontinued,[106] and Sentence discussions became read-only.[107] The change has been criticized on some online sites, such as Reddit.

In January 2023, Duolingo's data on over 2.6 million users' usernames, names, and phone numbers was sold in a hacker forum. Duolingo later stated that they would investigate the "dark web post".[108] They concluded that the data was obtained by scraping publicly available information based on an exposed application programming interface (API).[109] [110] Duolingo's spokesperson states that the API is intentionally publicly visible.

Since the end of October 2023, Duolingo has stopped updating its Welsh course to "focus on languages in higher demand". Some users criticized this decision because it came at the expense of learners of a language with limited resources on the market and the potential halting of the Welsh Government "Cymraeg 2050" strategy to promote Welsh language learning.[111] [112]

Awards

In 2013, Apple chose Duolingo as its iPhone App of the Year, a first for an educational application.[113] That year, Duolingo ranked No.7 on Fast Company "The World's Most Innovative Companies: Education Honorees" list "for crowdsourcing web translation by turning it into a free language-learning program".[114] [115] [116] Duolingo won Best Education Startup at the 2014 Crunchies,[117] [118] and was the most downloaded 'education app' in Google Play in 2013 and 2014.[119] In July 2020, PCMag named it "The Best Free Language Learning App".[120]

As a company, Duolingo has likewise won several awards and recognitions. In 2015, it was announced as that year's Index Award winner in the Play & Learning category by The Index Project.[121] It won Inc. magazine's Best Workplaces 2018,[122] made Entrepreneur magazine's Top Company Culture List 2018,[123] was among CNBC's "Disruptor 50" lists for 2018 and 2019,[124] [125] [126] and was ranked as one of TIME magazine's 50 Genius Companies.[127] Duolingo was named one of Forbes "Next Billion-Dollar Startups 2019".[128] In 2023, Duolingo won a Design Award during the 2023 edition of the Apple Design Awards.[129]

Image and brand

Duolingo's characters

Duolingo has brand characters that were used for engagement. Some of these characters include Duo the Owl, Lily, Zari, Eddy, and Vikram.[130]

Popular culture

Due to the app's frequent reminder notifications, Duolingo's mascot, a green cartoon owl named Duo, has been the subject of Internet memes depicting him as "evil" and stalking and threatening users if they do not keep using the app.[131] [132]

Duolingo has leaned into its online reputation and has adjusted its social media and marketing strategies accordingly.[133] Acknowledging the meme, Duolingo released a video on April Fools' Day 2019, depicting a facetious new feature called "Duolingo Push". In the video, users of "Duolingo Push" are reminded to use the app by Duo himself (depicted by a person wearing a Duolingo mascot costume), who stares at and follows them until they comply.[134] [135] It was also acknowledged during Duolingo's 2022 April Fools' Day video, "Lawyer Fights Duolingo Owl for $2,700,000", where a fictitious law firm fights for those that have been harmed by Duolingo's owl mascot.[136] This was further referenced by the company in its 2024 April Fools' Day skit "Duo on Ice", in which the owl, in a mix of Spanish and English, admitted to having an appetite for human flesh, and if the user failed to continue their streak, they would "eat their head like a praying mantis."[137] In February 2020, as part of the company's partnership with Angry Birds 2, a skit video depicting Duo and the red Angry Bird attacking people was uploaded.[138]

In November 2019, Saturday Night Live parodied Duolingo in a sketch where adults learned to communicate with children by using a fictitious course called "Duolingo for Talking to Children".[139]

The 2023 film Barbie contains a running gag where the husband of disgruntled Mattel employee Gloria uses Duolingo to learn Spanish, Gloria's native language.

Duocon

Duocon is an annual event organized by Duolingo. It sometimes published updates and wrote about new features from Duolingo.[140]

Offices

Duolingo is headquartered in Pittsburgh, Pennsylvania, and has offices in Seattle, New York, Detroit, Beijing, and Berlin.[141]

See also

Notes and References

  1. Web site: Duolingo, Inc. 2023 Annual Report (Form 10-K) . 2024-02-29 . . March 1, 2024.
  2. Web site: Migrating Duolingo's Android app to 100% Kotlin . blog.duolingo.com . 2020-04-06 . September 17, 2020 . December 23, 2020 . https://web.archive.org/web/20201223023826/https://blog.duolingo.com/migrating-duolingos-android-app-to-100-kotlin/ . live .
  3. Web site: Real World Swift – Making Duolingo Blog . making.duolingo.com . 2015-01-07 . October 22, 2018 . June 6, 2019 . https://web.archive.org/web/20190606014131/https://making.duolingo.com/real-world-swift . live .
  4. Web site: Rewriting Duolingo's engine in Scala – Making Duolingo Blog . making.duolingo.com . 2017-01-31 . February 1, 2017 . August 4, 2019 . https://web.archive.org/web/20190804123312/https://making.duolingo.com/rewriting-duolingos-engine-in-scala . live .
  5. Web site: Ortiz . Sabrina . Duolingo opens waitlist for its new, free music course. Here's how to sign up . live . https://web.archive.org/web/20231012040140/https://www.zdnet.com/article/duolingo-opens-waitlist-for-its-new-free-music-course-heres-how-to-sign-up/ . October 12, 2023 . 2023-10-11 . ZDNET . en.
  6. Web site: Duolingo Team . 2022-10-26 . Duolingo Math makes learning easy as pi(e) . live . https://web.archive.org/web/20221027114012/https://blog.duolingo.com/duolingo-launches-math-app/ . October 27, 2022 . October 27, 2022 . Duolingo . en.
  7. Web site: Higgins-Dunn . Noah . 2019-04-14 . If you are a 'Game of Thrones' fan, this app will teach you how to speak in High Valyrian . 2022-05-23 . . en . November 12, 2019 . https://web.archive.org/web/20191112051445/https://www.cnbc.com/2019/04/14/game-of-thrones-fans-this-app-teaches-you-to-speak-in-high-valyrian.html . live .
  8. Web site: 2023-12-26 . Dear Duolingo: Why is spaced repetition so important for learning? . 2024-08-02 . Duolingo Blog . en.
  9. Web site: duolingo reports 45% revenue growth and record profitability in first quarter 2024; raises full year guidance .
  10. Web site: Ceci . Laura . Top language learning apps by downloads 2023 . live . https://web.archive.org/web/20240120095059/https://www.statista.com/statistics/1239522/top-language-learning-apps-downloads/ . January 20, 2024 . 2023-10-06 . Statista . en.
  11. Web site: Transcribing . Motley Fool . 2024-08-07 . Duolingo (DUOL) Q2 2024 Earnings Call Transcript . 2024-08-09 . The Motley Fool . en.
  12. Shortt . Mitchell . Tilak . Shantanu . Kuznetcova . Irina . Martens . Bethany . Akinkuolie . Babatunde . 2023-03-04 . Gamification in mobile-assisted language learning: a systematic review of Duolingo literature from public release of 2012 to early 2020 . Computer Assisted Language Learning . en . 36 . 3 . 517–554 . 10.1080/09588221.2021.1933540 . 0958-8221. free .
  13. Web site: Cohen . Ben . June 14, 2024 . The Only App That Always Wins the Battle for Your Attention . The Wall Street Journal.
  14. Web site: Morley . Olivia . 2024-04-05 . Duolingo's Masterminded Social Listening Tactics . 2024-06-18 . www.adweek.com . en-US.
  15. News: Meet Duolingo, Google's Next Acquisition Target; Learn A Language, Help The Web . . M.G. . Siegler . 2011-04-12 . 2014-11-21 . November 29, 2020 . https://web.archive.org/web/20201129162336/https://techcrunch.com/2011/04/12/duolingo/ . live .
  16. Web site: Loeb . Steven . 2018-06-22 . When Duolingo was young: the early years . live . https://web.archive.org/web/20180625024407/https://vator.tv/news/2018-06-22-when-duolingo-was-young-the-early-years . June 25, 2018 . 2019-12-21 . VatorNews.
  17. Web site: Ahn . Luis von . Luis Von Ahn's answer to What made Luis Von Ahn start Duolingo? . live . https://web.archive.org/web/20240222194940/https://www.quora.com/What-made-Luis-Von-Ahn-start-Duolingo/answer/Luis-Von-Ahn . February 22, 2024 . 2021-05-14 . Quora.
  18. Web site: Olson . Parmy . Crowdsourcing Capitalists: How Duolingo's Founders Offered Free Education To Millions . live . https://web.archive.org/web/20140127012240/https://www.forbes.com/sites/parmyolson/2014/01/22/crowdsourcing-capitalists-how-duolingos-founders-offered-free-education-to-millions/ . January 27, 2014 . August 26, 2017 . Forbes.
  19. Web site: October 27, 2023 . Duolingo creator to be inducted into Inventors Hall of Fame . live . https://web.archive.org/web/20231102231928/https://www.nbcnews.com/now/video/duolingo-creator-to-be-inducted-into-inventors-hall-of-fame-196504645525 . November 2, 2023 . 2023-11-02 . NBC News . Video.
  20. Web site: Lee . Dami . 2018-12-13 . Duolingo redesigned its owl to guilt-trip you even harder . live . https://web.archive.org/web/20240329050328/https://www.theverge.com/2018/12/13/18137843/duolingo-owl-redesign-language-learning-app . March 29, 2024 . 2024-06-06 . The Verge . en.
  21. Web site: Ahn . Luis von . 2017 . Online Education as a Vehicle for Human Computation . live . https://web.archive.org/web/20160304110021/https://www.nsf.gov/awardsearch/showAward.do?AwardNumber=1054630 . March 4, 2016 . April 6, 2018 . U.S. National Science Foundation.
  22. News: Masson-Forsythe . Heather . December 22, 2022 . NSF gave Duolingo its wings! . live . https://web.archive.org/web/20230325173930/https://beta.nsf.gov/science-matters/nsf-gave-duolingo-its-wings . March 25, 2023 . 25 March 2023 . . en.
  23. Giles . Jim . January 11, 2012 . Learn a language, translate the web . registration . live . https://web.archive.org/web/20150428034914/http://www.newscientist.com/article/mg21328476.200-learn-a-language-translate-the-web.html . April 28, 2015 . August 26, 2017 . New Scientist.
  24. Web site: Lardinois . Frederic . 2015-06-10 . Duolingo Raises $45 Million Series D Round Led By Google Capital, Now Valued At $470M . live . https://web.archive.org/web/20150804225710/http://techcrunch.com/2015/06/10/duolingo-raises-45-million-series-d-round-led-by-google-ventures-now-valued-at-470m/ . 4 August 2015 . 2019-12-14 . . en-US . Instead, the company is now using its Test Center certification program as a revenue source (the tests cost $20) and says that it has other plans to monetize..
  25. Web site: Ahn . Luis von . May 12, 2022 . (anonymous) . Duol shareholder letter 2022 . live . https://web.archive.org/web/20220512201622/https://investors.duolingo.com/static-files/d667f9d1-8f7f-418c-b116-e699a30a9826 . May 12, 2022 . May 28, 2022 . DOC.
  26. News: The Daily Start-Up: Kutcher-Backed Language Site Duolingo Finds Its Voice . 2012-07-13 . . 2012-06-19 . April 3, 2019 . https://web.archive.org/web/20190403191839/https://blogs.wsj.com/venturecapital/2012/06/19/the-daily-start-up-kutcher-backed-language-site-duolingo-finds-its-voice/ . live .
  27. Web site: Duolingo will translate the internet while teaching languages . Adi . Robertson . 2011-12-16 . . 2016-02-03 . January 8, 2012 . https://web.archive.org/web/20120108020114/https://www.theverge.com/2011/12/16/2639262/duolingo-translate-internet-teach-languages . live .
  28. News: Loeb . Steven . 2018-06-22 . When Duolingo was young: the early years . live . https://web.archive.org/web/20180625024407/https://vator.tv/news/2018-06-22-when-duolingo-was-young-the-early-years . June 25, 2018 . 2019-12-14 . VatorNews . Duolingo's Third Year.
  29. Web site: Spice . Byron . Press Release: Duolingo.com Users Will Translate Web As They Learn a New Language . live . https://web.archive.org/web/20120826233724/http://www.cmu.edu/news/stories/archives/2012/june/june19_duolingo.html . August 26, 2012 . 2021-05-14 . . en.
  30. Web site: Duolingo Raises $15M Series B Round Led By NEA, Will Expand To More Languages And To Mobile Soon . . 2012-09-17 . en-US . 2019-12-13 . 14 December 2019 . https://web.archive.org/web/20191214003206/http://social.techcrunch.com/2012/09/17/duolingo-raises-15m-series-b-round-lead-by-nea-will-expand-to-more-languages-and-to-mobile-soon/ . live .
  31. Web site: Language Learning Service Duolingo Launches Its First iPhone App . Frederic . Lardinois . 2012-11-13 . . . 2016-04-18 . November 13, 2012 . https://web.archive.org/web/20121113205450/https://techcrunch.com/2012/11/13/language-learning-service-duolingo-launches-its-first-iphone-app/ . live .
  32. Web site: Free Language Learning Service Duolingo Comes To Android . 2021-05-14 . . 2013-05-29 . en-US . 14 May 2021 . https://web.archive.org/web/20210514230149/https://social.techcrunch.com/2013/05/29/free-language-learning-service-duolingo-comes-to-android-expects-this-will-double-its-user-base-to-over-6m/ . live .
  33. Web site: Duolingo brings free language courses to the iPad . Farber . Dan . 2013-07-11 . C net . 2014-02-21 . August 20, 2013 . https://web.archive.org/web/20130820163502/http://news.cnet.com/8301-1023_3-57593078-93/duolingo-brings-free-language-courses-to-the-ipad/ . live .
  34. Web site: Duolingo Raises $20M Series C Led By Kleiner Perkins To Dominate Online Language Learning . 2021-05-14 . . 2014-02-14 . en-US . 10 March 2015 . https://web.archive.org/web/20150310011231/https://social.techcrunch.com/2014/02/18/duolingo-raises-20m-series-c-round-led-by-kleiner-perkins-wants-to-dominate-online-language-learning/ . live .
  35. Web site: 100M users strong, Duolingo raises $45M led by Google at a $470M valuation to grow language-learning platform . 2015-06-10 . VentureBeat . en-US . 2019-12-14 . June 16, 2015 . https://web.archive.org/web/20150616221249/https://venturebeat.com/2015/06/10/100m-users-strong-duolingo-raises-45m-led-by-google-at-a-470m-valuation-to-grow-language-learning-platform/ . live .
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