Tell me who is the winner

.
I suppose that it is not really a 'mistake' any more, since it is in such common use. In careful writing though, I would avoid it.
.

Lcwangquite often we see sentence like:

Can anyone tell me who is the winner?

Is that a mistake, or is it also acceptable?

It's called semi-indirect speech, and it's less acceptable than indirect speech in my opinion.
I would stick with Can anyone tell me who the winner is?
CJ

Thank you very much, Mister Micawber and cj. But is it also alright to say:

I don't know who is she.

Since we can say: I don't know who is to blame. I think it should be OK to say: I don't know who is she., taking who as the subject of the noun clause. In the sentence I don't know who she is, who is the subject complement of the clause.

.
You can say it, LC-- though it has nothing to do with the blameworthy person-- but it is unacceptable in most quarters and considered uneducated.
.

I see. Thank you, Mr. Micawber.