I am trying to find the logic an in this case it seems to be this: In "Yine mi süt?" the question is in the again part as if one is surpised by the lack of variation. If one would say "Yine süt mü?" it would be more like asking if the person wants another milk, or if the person wants the usual drink which is milk. Please correct me if I am wrong.
"soru edatı mi'nin direkt çevirisi yoktur" is a note that means "there is no way to directly translate the question particle "mi" into English."
The little particle "mi" (and its other forms mü/mı/mu) are a way to ask questions when there's no other question word (yes/no questions generally).
Yine süt. = Milk again.
Yine mi süt? = Milk AGAIN?
It can also be moved to different places to emphasize different aspects in the question. In English we'd generally do this with intonation.
- Yine süt mü? = (Should it be) milk, again?