It might hang from a wall, but I agree hang on is odd when talking about a shelf.
For those who don't know: if something is flat against a wall (or chimney or similar), it hangs on (or against) the wall, but if it not flat against the wall and it proportionally sticks out, it generally hangs from the wall.
A single shelf hanging from a wall is still somewhat odd. A single shelf simply wouldn't be stable if hanging. A single shelf is normally mounted on a wall, as jairapetyan suggests.
A set of shelves could be hung on a wall though, like this, because the structure of the shelves would prevent a single shelf from falling over. If hyllan in this case is referring to a set of shelves, and the English translation is adjusted to "the shelves hang on the wall", it would also make sense.
I would change the English to "The shelf is mounted on the wall".
In my upbringing, if something is hung on a wall, it should be against the wall, not necessarily flat against it. Perhaps it's regional? I'm from Vancouver, Canada, with a British mother long naturalised and a Canadian father. We (my family/friends) wouldn't say that a shelf hangs from a wall unless there's a space between the object and the wall, as something hanging from a hook that sticks out. Though in that case we'd also be inclined to be more precise and say "hanging from a hook in/on the wall". In speaking of a wall-hung shelf, I would automatically say "hangs on the wall". Perhaps it's partly in the meaning of the word hang, which has several correct definitions, such as 1.1 and 1.2 in the Oxford English dictionary: http://www.oxforddictionaries.com/definition/english/hang
Actually "hang on" is better. "Hang from" implies that it's loose, so favoring "from" refers to an exceptional situation. It is possible to hang a shelf on the wall if it is fastened with hooks. I have a knick-knack shelf hanging on my kitchen wall. No way would I want it hanging from the wall like those dangling bottles in a song that some one else here mentioned.
I concur with photodiarist and pekarekr. I came to this thread because “hangs from the wall” sounds distinctly wrong to me. To “hang from” something, an object would need to be dangling away from its stated support. An object can hang from a ceiling, or even from a hook on a wall, but not from a vertical surface itself; a thing can jut out away from a wall, but not hang from it. The phrasing has to follow our sense of gravity.
There is absolutely nothing wrong, on the other hand, with “the shelf hangs on the wall.” If something appears to hug the wall, it can be said to be “on the wall”. Contrary to "hanging from", the hanging aspect here does not indicate dangling; it merely expresses that the object does not extend all the way down to the floor and gets its support instead from the wall. “Hanging on the wall” means attached to the wall by whatever means, and not limited to one point of support. I imagine “hänger på väggen” carries the same idea.
I've honestly given up on trying to make this sentence idiomatic in English. If you look up, you'll see that e.g. Mark the Muppet and jairapetyan both dislike "on", and they're native English speakers whose judgement I trust as much as I do yours.
I can't remember if I did frequency counts the last time I revised this sentence. To be clear, both "on" and "from" are accepted, but I don't think I'll even find a single version I can use to please everybody.
It doesn't matter how many agree/disagree. It matters that a correct tranlation in English is available. People hang shelves ON walls, not FROM them. A quick google search on how to hang shelves will show a myriad of sites showing how to hang shelves on tiled walls, cement walls, brick walls, wooden walls.
As a native English speaker as well as a total geek about the English language (have my own private proofreading/copy editing company as well as my regular day job), I'm pretty certain about this one.
With respect, RevShirls, if this course has taught me anything, it is that there often is no such thing as "correct English". I have no doubt that you are very good at the specific English you speak. You've given me no reason to think anything else, and I do not doubt that you are a competent proofreader. I also have no doubt that a very large number of users I respect greatly are equally good at the specific English they speak.
It is supremely annoying that you lot keep disagreeing with each other. There has been no shortage of discussions between native English speakers likely better versed in the language than you and I both on these forums. I cannot accept that some of these users get to dictate to others how to use their own language. And it does matter how many agree or disagree. It's the essential premise for how to categorise "correct English", even if preferrably on a larger scale than here.
Not to beat a dead horse, I would like just to add the observation that those who take exception to "hangs on the wall" do so out of a too-narrow interpretation of the verb "hang" -- that a hanging item must take a single point of support from above and therefore its stability would be in question in the case of a hanging shelf. The definitions that aptly apply to this sentence, though, are listed in the 1971 edition of the Oxford English Dictionary as #12 -- "To remain suspended without visible support" and #14-b -- "To attach oneself for support. Of things: to stick, adhere, cleave". For comparison, OED gives this citation from Tyndall's Glacier (1860): "Secondary glaciers ... hanging on steep slopes." Take a look here at such a sight -- https://www.usgs.gov/centers/norock/science/secondary-glacier-network?qt-science_center_objects=0#qt-science_center_objects.
Hi Devalanteriel! To be honest, I'm amazed you lot haven't gone bonkers. I'm studying Scottish Gaelic on Duolingo as well as Spanish (just started the Spanish as my daughter is learning Spanish at school). The Spanish forum gets similar questions but the Gaelic forum is extremely calm with very little, if any, disagreement - probably because the "course" uses very literal (sometimes awkward) English sentence constructions as a way of teaching.
I am actually amazed by the quality of your English and your knowledge of etymology in both languages.
As for this particular question, I'm sticking to my guns. My daughter has autism level 1 and I'm beginning to think I have it too. There are things I just can"t let go. By the way, you don't need to reply to this.
LelandSun: Couldn't agree more with all your points.
I agree that "Hangs from the wall" sounds distinctly wrong because no one says it. If you google "the shelf hangs on the wall" you will get hits. If you google "the shelf hangs from the wall" you will get ZERO hits because no native speaker of standard English would ever say that. What you will find is "how to hang shelves ON a wall" and you will NOT find "how to hang shelves from a wall." Any doubters should try the Google search on their own.
You are also correct in saying that an object can hang from the ceiling, or from a hook. To hang from is to be suspended from or dangle, and shelves don't dangle.
Agreed. One does not typically say the (insert noun) hangs from the wall unless one says that the (insert noun) is hanging (insert direction) from the wall. Although grammatically correct I would rarely hear a native English speaker say many things hang from the wall without a direction. At a minimum it seems Duolingo would allow both answers.