Duolingo Offline Mode becomes less usable as you progress
**UPDATE 2019 August **
I'm appending a comment to this video to state that Duolingo has addressed this problem and added additional Japanese lessons. But, the Internet is an archive. So I am leaving the video in place with this comment.
Original Description:
Duoplingo is an excellent application for breaking the ice on learning a foreign language. The application is free with ads, but one can upgrade to the Plus level to remove the ads and allow the lessons to be used even when there is no data connection on the device.
However, as one masters a kill level it becomes no longer available for offline use. As I've progressed through Duolingo I've found this has the effect of eroding the offline functionality for my language of choice progressively towards nonexistent.
I've made this video to explain this to someone else. I hope that Duolingo addresses this.