The most idiomatic translation would be skulle vilja, I think, literally would want/like.
- I wish to make a complaint. = Jag skulle vilja framföra ett klagomål.
- I wish to leave now. = Jag skulle vilja gå nu.
“She wants a horse” is not accepted. What is the difference in meaning that makes “…wants…” not a good fit for “…önskar sig…” here?
i think 'önskar' stands for fantasy more than an actual physical want because for want we use 'vill ha'
Then you'd be more likely to say "she would like to have". "Wishes for" isn't an expression i can see anyone actually using in this context - sounds antiquated.
Like Portuguese that “skulle vilja”, although Portuguese has already a conjugation to that as “queria - would want”, “queria um livro - jag skulle vilja en bok”, so, I think that's good to me :D
"I would want" is "Eu quereria" (futuro do pretérito - "future's past"), that one may say as "Eu iria querer". "I wanted" is be "Eu queria" (pretérito imperfeito - "imperfect past"); "Eu quero um livro." - "I want a book." - "Jag vill ha en bok."
"Jag önskar" is "Eu desejo/Eu gostaria de", and, in english, "I wish/would like"; "Eu desejaria/gostaria de um alce." - "I wish for/would like a moose" - "Jag önskar sig en älg."
I hope that is correct. :)
I see you're trying to draw similarities to the use of "till" in "ägg till frukost" (eggs for breakfast) but these are different contexts, and while in English the grammatical constructions are the same (in regards to the use of "for"), the inderlying ideas are what need to be conceptualized differently in order to create sensible Swedish translations. Simply practicing the different uses of prepositions in various contexts should help. Not a native Swedish speaker, but this is my perspective.
so, what would be the difference in meaning if someone said "Jag önskar mig en häst", "Jag vill ha en häst" and "Jag vilja en häst". Don't all three things mean the same, that he wants a horse?
The first two basically yes, but Jag vilja makes no sense because it is the infinitive, unconjugated form of the verb.
What is the function of "sig" here? If she wished for a horse for someone else, would that person replace "sig?"
It does men she wishes it for herself. You can wish "feelings" for other persons, like "jag önskar honom en trevlig resa"-"i wish him a pleasant trip". However, you don't normally say "jag önskar honom en häst", in that case you probably say "jag hoppas han får en häst" - "i hope he gets a horse".
I think the "sig" it the she wishes for herself, but I don't know if it was a wish for someone else you write something else.