I find Duolingo is pretty good for vocabulary in a "slow" context. The trouble is, that slow context is already better served by translation apps. Duolingo is

I find Duolingo is pretty good for vocabulary in a "slow" context. The trouble is, that slow context is already better served by translation apps. Duolingo is really bad at developing verbal fluency, which is the thing you actually need in today's world of translation apps.