Offline content when skill tree is finished
I commute to work on the underground (no wifi/internet) and this is the only time I have to use duolingo. It was fine before I finished the spanish tree as I could do the lessons offline, but since I have finished it, I cannot use the app, as there are no offline lessons for the finished tree.
PLEASE let us mark lessons to keep offline so we can continue practising once we have finished the tree.
Maybe start a reverse tree (english from spanish) - you learn more spanish than just doing the normal tree (imho).
That reverse tree starts out easy but soon mixes challenges into mix. For instance the subjunctive in Spanish shows up very early in the English tree.