Duolingo was updated so that the main user interface no longer shows how well Duolingo thinks the user knows the different skills. Furthermore, there is no encouragement (in terms of skills turning golden) for practicing weak skills.
These features were replaced by skill levels (crowns), which one can earn by exercising the skills. At higher level skills the exercises get more difficult, or at least there is more translating into the learned language and less into the language one is learning from.
How can one combine the new Duolingo system with spaced repetition?