Pronunciation of Y
All the web sites I see give the pronunciation of Norwegian y as IPA:[y] (as French u or German ü), making a special point to remind the reader that the lips should be extended rather than compressed. However, in every Norwegian medium I have heard, y sounds exactly like [i]. In one of the Duolingo phrases, it even gets shortened to [ɪ]!
Does this vary with dialect (e.g., pronunciation closer to [i~ɪ] being more common in, say, vestnorsk or Trøndersk), or is it simply my untrained ear not hearing the difference?
Y and I are indeed quite similar sounding, it could also be that the robotic voice does a poor job distinguishing the two sounds.
It get's really obvious once you look at someone's mouth pronouncing the two. So I wouldn't worry, you will spot the difference sooner or later.
Thinking of the Y more like the German ü should help quite a bit, as they are fairly similar sounds.
To my knowledge, the pronunciation of Y does not vary with dialect.