Duolingo and many other apps avoid the hardest and most essential skill: translating from your language to the other. It's often easy to guess what words mean especially with the help of cognates and other similarities between languages. 99% of Duolingo mobile is like this. Even when you see words in your language first, your task is to tap the presented foreigin words in order. You'll never learn to speak this way.…
The hardest and most essential skill, second only to: not translating from your language to the other :)
(or maybe it should be the other way around; translating is useful but a really hard crutch to kick. Keeping it around will make it hard to keep up while speaking/listening and make reading a slog)