GUEST,

I doubt that. These two lines absolutely don't suggest any repetitiveness. The grammar indicates an action to take place in the future only once. 'We'll unwind a curly birch,' once, end of story.

Doesn't make a whole lot of sense as is, but in Russian poetry "birch tree" often stands for "girl/woman" — and it's anybody's guess what "unwind" could mean in this context if that's the case here.

Lighter,

From what I've heard, the tune is mostly authentic trad while the lyrics have been seriously doctored. Makes sense to me. It's hard to believe anyone would risk bringing the lowly language the original lyrics are told to pretty much consist of into the high society in the middle of the 19th century.