You earn crystals as you complete lessons. You can buy more from the Shop tab

Duolingo Plus lets you download lessons offline and removes ad. You can start with a 7 day trial

It quizzes you with audio and visual questions to make you understand and to increase recall

You can tap the country flag on top to add more languages and switch between them

Achievement leveled up modal

The splash screen is the logo on a green background

There are posts by other learners and mini "games" that help you test your skills

First lesson complete. It shows your learning minutes and asks you to create a profile

The curriculum is arranged linearly as a timeline with tests interspersed in between

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Bottom sheet with total minutes when you complete a session