Duolingo is a popular mobile language-learning application that has been around the market since 2012 and has been researched in its language-learning abilities. It is crucial for mobile language learning applications to keep their users interested, nevertheless, as users easily lose interest in continuing their language study. This thesis looks at how Duolingo's gamified system design implements persuasive principles to increase user engagement. The thesis aims to advance the knowledge of user engagement in language learning apps and help create useful mobile language learning applications. To achieve the goal, it was necessary to determine which persuasive principles were being applied by Duolingo's gamified system design. This was done using the Persuasive System Design (PSD) model by Oinas Kukkonen and Harjumaa (2009). The research consisted of qualitative semi-structured interviews with 8 young adults living in Sweden. The aim of the interviews was to find detailed, deep, empirical data and compare it to a theoretical framework using thematic analysis. The results of these interviews showed that Duolingo's gamified system design effectively applies persuasive principles to engage and encourage language learners. However, it was discovered that several persuasive principles needed to be improved in order to further enhance user involvement. This study adds to the understanding of persuasion by demonstrating how these principles can be applied to other mobile language learning applications to increase user engagement.

Duolingo is today the most popular app when it comes to language learning. Gamification plays a major role in increasing the motivation of Duolingo's users. Duolingo has a strong graphic identity that has been developed over the past ten years and in this paper, I investigate how they with the help of colour and shape that help the gamification elements to strengthen the motivation of the user. Because there are so many different gamification elements in Duolingo, it is the "skill-tree" and the app's front page that are the focus of the analysis. The results show that Duolingo has a very well thought out design that is simple but powerful with a lot of symbolism that originates from ancient cultures where the symbolism from both icons and colours has wide meanings and can be decoded by people from many different cultures and backgrounds.