I'm learning French and Ukrainian in Duolingo. And I have noticed that French has so lessons when compared to Ukrainian. Why is this difference? Are they going to increase the number of lessons in near future? Or the current number of lessons is enough to be a decent speaker?
This difference is because Duolingo allocate extra resources to a handful of languages, notably Spanish, French, German, and Portuguese. This is probably because these languages tend to be taught more often in the English speaking world.
Officially for updates on the courses we should look at the incubator: https://incubator.duolingo.com/courses/uk/en/status
The current number of lessons will probably not be enough to make you a decent speaker, but this is generally true of most internet courses. If I recall correctly it teaches somewhere between 1000 and 1500 words.