What is wrong with, "Miksi japani kaunis kieli on" as an answer? I thought the "on" appeared at the end in questions.
From what my finnish gf told me, you put the question word at the beginning, then proceed like a normal sentence that wouldnt be a question: japani on kaunis kieli
It's usually not tho.
Technically it's not incorrect but it makes it sound poetic. Not very natural.
I don't know where you got that idea but that is not a rule. A subject predicative ideally is separated from the subject by the copula, i.e. the linking verb.
OP saw "millainen kieli tämä on" and figured the verb should be last.
Why not "Miksi on japani kaunis kieli"? It was marked as wrong
Finnish does not require a subject-verb inversion for questions when the question begins with an interrogative word instead of a verb.