Yes, 语鹿 is free to download, however it contains in-app purchases or subscription offerings.
Not enough reviews to make a reliable assessment. The app needs more user feedback.
语鹿 has several in-app purchases/subscriptions, the average in-app price is €2.32.
To get estimated revenue of 语鹿 app and other AppStore insights you can sign up to AppTail Mobile Analytics Platform.