For certain activities, you unlock Achievement Badges. Some of these are Inner Circle, Sharpshooter, Big Spender, Overachiever, Overtime, Friendlt, Wildfire and Champion.

Each badge has 3 levels that you progressively unlock.

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Duolingo

Duolingo Plus
Onboarding
Change or add language
Gamification memes
Asking for notiification permissions during onboarding
Duolingo Clubs
App icon change
Learning experience
Create profile
Top level tabs
App Store screenshots
Gamification: Streak, Lives and Gems
2019 redesign

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Gamification

Gamification with the translation camera
Blitz Buy gamification
Gamification: Streak, Lives and Gems
Daily check ins