"The beautiful song is Russian."
Translation:Kaunis laulu on venäläinen.
"Biisi" is a loanword (piece) and it's used in spoken Finnish and more informal written texts. The Finnish equivalent of "biisi" is actually "kappale" and not "laulu". A "biisi" or "kappale" is a musical piece that can have singing in it, or not, while "laulu" is related to the verb "laulaa" (to sing) and thus translates to "a song".
Thank you for the explanation. The reason I was asking, is the course uses both, and the translation is exactly the same. It is easier to follow which one to use in the same section, but when it comes to "practice" part, it is pretty much impossible to tell the difference. I wish it was either one or the other everywhere, or both were universally accepted to make it easier for the learners. Also, "piece" is a totally legit word in musical sense in English, not sure why it wasn't used to make that distinction.