public offering on NASDAQ under the ticker DUOL. From August 2021 to June 2022, the Duolingo language learning app was removed from some app stores in China. In the early 2020s, Duolingo was noted for their viral videos on the social media platform TikTok. In August 2022, Duolingo overhauled its user interface and user experience, changing the structure of the courses from a tree-like design where users could choose from a range of lessons after completing previous ones, to a linear progression. This was widely criticized by users across a variety of social media outlets, including Reddit and Twitter. CEO Luis von Ahn said that they had no plans of undoing the changes, commenting that their decision was made in order to simplify Duolingo for new users, and that maintaining both the old and new versions would be difficult. In October 2022, Duolingo acquired Detroit-based animation studio Gunner. Services Duolingo Language app Lessons can include matching, translating, speaking, multiple choice or stories. This feature consists of a small story for a particular situation to help improve learners reading and listening skills. Stories are available on selected, most popular courses. For some languages Duolingo offers podcasts for people in intermediate level consisting on stories told usually by native speakers from different parts of the world where the target language is spoken, but with simplified grammar, vocabulary, and with a slower intonation, as well with occasional assistance with providing context or explanations of unusual words in the source language by a narrator. Duolingo also provides a competitive space. In Leagues, people can compete against their friends or see how they stack up against the rest of the world in randomly selected groupings of up to 30 users. Rankings in leagues are determined by the amount of XP earned in a week. Badges in Duolingo represent achievements that are earned from completing specific objectives or challenges. Duolingo provides features designed to allow teachers to track students' progress in language acquisition. Languages offered Duolingo provides language courses in many languages, including constructed languages such as High Valyrian (A Song of Ice and Fire) and Klingon (Star Trek). Duolingo offers courses in the following languages to speakers of English: Arabic Catalan Chinese (Cantonese) Chinese (Mandarin) Czech Danish Dutch English Esperanto Finnish French German Greek Guaraní Haitian Creole Hawaiian Hebrew High Valyrian Hindi Hungarian Indonesian Irish Italian Japanese Klingon Korean Latin Navajo Norwegian Polish Portuguese Romanian