Trivial, but the Dutch course is using the wrong flag!
Quite simple, but the flag on the Dutch course is not the Dutch flag. I had the very same mistake pointed out to me on facebook a couple of days ago - the flag you have attached to that course is the flag of Luxembourg.
It's notoriously difficult to tell the two apart - but the blue stripe on the Dutch flag is dark blue, almost Navy.
Dunno if it's something you can correct (or even want to bother correcting), but you should if you can :)
I don't think it's that the flag is Luxembourg's one, but merely that Duolingo uses the exact same cartoonish blue colour for all its flags.
Here is the image Duolingo uses for displaying each of the course flags:
I agree it's not right though. It's certainly odd that the blue on the Netherlands' flag is the same as say the blue on Tanzania's flag. ^^;
Almost makes me glad now that they used the USA's flag for English... I dread to think what it would have looked like if they'd went with the British flag and coloured it in with that garish shade of blue! :P
And I just noticed that the Korean flag has the bright blue at the bottom part of the Taegeuk instead of the normal dark blue, and the Czech flag has bright blue on the left side instead of the normal dark blue, same with the French flag.
Well, I'll be curious to see what Duolingo will do if they ever decide to make a Luxembourgish course...