"What kind of country is Sweden?"
Translation:Millainen maa Ruotsi on?
That has a slightly different meaning. Ruotsi is then the predicate, not the subject of the verb. While technically possible, the scenarios where you would use this structure are pretty far-fetched. Switch out "to be" with a similar verb ("what kind of country would be considered/is equal to Sweden?") and you'll see what I mean.
The word order in Finnish is pretty much free and certain word orders or in certain contexts they can sound a bit off (or poetic) to a Finn's ear but there is no as strict rules as with some languages (German for example). I wouldn't say this is particularly wrong, I'd prefer having the verb at the end but if you use this sentence when talking to a native (which I also am!), I can promise you that you won't be misunderstood.
///Edit 2: I think I just cracked the code - I figured it must be because of the interrogative word since in Finnish it won't change the word order, the verb still comes after the subject, and that's why it is at the end of the phrase! I can see this happening with most interrogative phrases when I think of it.
///Edit: I don't speak Estonian and I know nothing about the rules or grammar of that, but I wonder if my explanation is any similar to how the difference is in Estonian? :D All I remember reading is that Estonian uses some older things in their grammar that Finnish got rid of long time ago.
I must say I still don't quite get it. Maybe it is because I'm trying to compare it to Estonian which would be "Milline maa on Rootsi? or "Milline maa Rootsi on? and I can't see the difference...maybe only tiny, not sure. I guess that happens when your native language is too similar, you go by inner feeling not by grammar.
Again these positional questions need addressing it does not matter in which order the subject is!!
Millainen maa on ruotsi is identical to Millainen maa ruotsi on.
In fact it's debatable whether the former is actually common at all.
Either way both are more than acceptable, and now there has been previous comments about the same issue.
-ko/-kö is the suffix that indicates a question, but you can't use it in that place because "millainen" is already the interrogative word. You can use "onko" at the beginning of the phrase, though, for example: "Onko Ruotsi millainen maa?" (But I have no idea if Duolingo accepts that already/yet... but in real life both work just fine.)