"It is Sunday tomorrow."
Translation:Det är söndag i morgon.
It is not just a thing of the Germanic languages. Tomorrow in French (demain) and Italian (domani) come from Latin de mane (of morning). Also the Russian завтра comes from за + утро (of morning). Even the Finnish huomenna has the old world huomen (morning) as its root.
Why? See you in the morning! => See you tomorrow. I will do it in the morning. => I will do it tomorrow.
I notice you've mentioned this recommendation a few times. Do you know the reason /why/ they recommend the separation of imorgon, idag, etc, into i morgon, i dag, etc? Is the contraction an archaic construction they're trying to discourage, or conversely is it a modern thing they want to stamp out? :)
I get the feeling the Språkrådet* would like to have the same power over Swedish as the Nederlandse Taalunie does over Dutch (and, to a lesser extent, Flemish) or l'Académie française does over French, but doesn't.
(* Is it still tautological if you're crossing languages?)
The reason is that some combinations like this cannot be written together, only apart (e.g. i övermorgon, i förrgår), so it is easier to get them all right if you write them all apart. – But they're very clear that both ways are perfectly correct.
I did a search in old texts (from ca 1600-now) and the picture is very scattered. Both idag and i dag seem to appear throughout all times, but i dag is much more frequent.
I've read a lot of answers from Språkrådet and my impression is rather the opposite from what you're saying. They're very reluctant to be perceived as normative. They hardly ever say that anything is 'wrong'. The anti-normative trend in linguistics is very strong here, and it's been for a long time.
Writing words apart (särskrivning) is probably the most discussed issue in Swedish spelling, I mean among people who aren't linguists or language teachers. A lot of people tend to write compound words apart wrongly, and others snigger. Today we're also seeing more and more of the reverse side of that, people hyper-correctly writing words together when they should actually be written apart. However, what most people don't know is that 'särskrivning' is very old in Swedish. It's easy to find tons of examples in really old texts, where the spelling was less standardized (like 17-th and 18th century). Then there are fewer instances of it during the 19th and 20th thanks to correctors and standardized spelling, but more again today when people write with less control again.
One reason this happens is that it's actually hard or impossible to hear the difference. Whether compound words should be written together or apart is just a convention. English chose to write word list and Swedish chose to write ordlista, but that's pretty arbitrary. The same with igår vs i går. Is i a preposition or a part of the word? It's mostly just a question of convention, so of course there'll be variation. – Sorry for this long-winded answer, I'll see myself out now! ;)
No, it's good, I find it genuinely interesting! :)
I've read a lot of answers from Språkrådet and my impression is rather the opposite from what you're saying.
Woo, I can like them again! :D
people hyper-correctly writing words together when they should actually be written apart
I actually find myself doing this more and more in English with hyphenations and the (few) compound words we actually do have—a five-year-old child vs a child that's five years old, etc. I often find myself putting a hyphen between five and years in the second and then mentally slapping myself. On a semi-related note, if you haven't seen it there's an amusing example of exactly this on Wikipedia:
Wouldn't the sentence 'I want to put a hyphen between the words Fish and And and And and Chips in my Fish-And-Chips sign' have been clearer if quotation marks had been placed before Fish, and between Fish and and, and and and And, and And and and, and and and And, and And and and, and and and Chips, as well as after Chips?
I'm assuming you were shown I morgon är det söndag which is 'another correct answer'.
det is not an article of söndag, it is a pronoun. You can see that more clearly in the main version, which is Det är söndag i morgon.
det is a formal subject, corresponding to it in 'It is Sunday tomorrow', and not referring to söndag.