Translation:It will be a hot night tomorrow night.
I morgen, bliver det en varm aften. My guess is that even in Danish it isn't a good sentence and needs a bit of editing.
Is the second 'aften' in this sentence meant only as a tongue twister or is it necessary?
Well, it would otherwise mean "It will be a hot night tomorrow," which wouldn't make complete sense.
I'm not sure which language you are talking about in your reply. I'm asking specifically about Danish.
In English repeating 'night' sounds strange to me. If the sentence was about anything else than 'night' it would be perfectly fine but when talking about a part of the day it seems redundant. 'Tomorrow' specifies the time frame when the hot night is supposed to occur, there's only one night in each day therefore specifying when the night occurs during the next day is nonsense. If I substitute 'tomorrow' by some other time specification it sounds even stranger (It will be a hot night the next day night, it will be a hot night on Friday night).
The most natural way to say it would be 'It will be hot tomorrow night' anyway.
It wouldn't be "It will be a hot night the next day night," though "It will be a hot evening next evening" sounds fine to me, although I probably wouldn't use the "next" because it's ambiguous (and generally I don't use "next" to refer to the day after). "Next" also doesn't sound right with "night" to me, which is why I used "evening" there.
Saying "It will be a hot night tomorrow" would be like saying "It will be a hot weekend next week." It doesn't really make sense to me anyway.
You're right, the 'next day' example is strange. I was just trying to stay as close to the meaning as possible. But consider the version with a weekday or even a specific date, then repeating night is just weird.
"It will be a hot weekend next week" sounds absolutely fine. What will be? A hot weekend. When? Next week. What doesn't make sense about that?
My point is that a sentence saying what will be (a hot night) and when (tomorrow) is fine. If the what was anything else than a night (a performance for example) there'd be a difference between when (tomorrow) and more precise when (tomorrow evening) but since what and more precise when are the same the repetition is redundant.
"It will be a hot weekend next week" doesn't sound right to me. I don't know. It just does. "There will be a hot weekend next week" or "The weekend will be hot next week" or something along those lines sound better to me. I think it's just because I feel that the actual subject of the sentence would be "next week" and it would make no sense equating the weekend with next week. If the subject were the hot weekend then it feels awkward to me not having a preposition or some sort of conjunction in that sentence -- something like "It will be a hot weekend in the period of next week", though more complicated, I would prefer.
I don't know, I'm not very good at explaining. Change, however, the ingredients of the sentence a bit, and you've got:
It will be a hot night Friday.
which doesn't sound right to me.
I don't know. To some people that might sound fine. I don't particularly like it though.
While grammatically correct, I would question the logical structure of this sentence. No one speaks like that, it should be "It will be a hot night tomorrow".