Hearing "one", or "oni" here is an illusion created by the two "n" sounds standing next to each other. It is really hard to separate them as two distinct sounds, so they get "amplified" as if one "n" bounces off the other one... The thing is, Polish speakers would probably totally avoid this difficult to pronounce combination by skipping the personal pronoun "On", and saying: "Nosi płaszcz".
No. It used to be accepted, but I decided that it's time to start expecting only the real correct translation. "nosi" doesn't actually translate to "is wearing". This is one of those rare verbs that show the difference between Present Simple and Present Continuous. "He is wearing" is "On ma na sobie" (literally 'he has on himself'). Which unfortunately hasn't been taught in this course.
Just like the English sentence "He eats meat", the Polish sentence "On nosi płaszcz" refers to the daily, regular "use"
of a coat. The verb "nosić" is an exception in a sense that it does not refer to the continuous state of "having it on" at
the present moment, that is now, as we speak.
The sentence "He puts the coat on" (He wears the coat") would translate to Polish: "(On) Zakłada płaszcz", because
it does refer to the short "act of putting the coat on".
I believe, Duolingo is at fault now, because it does not accept the concept of continuous wearing of the coat... after it is put on, rejecting the progressive form of the verb "to wear" and enforcing the use of the Simple Present tense as the only and "correct this time" translation for this scenario...
Hopefully, this misunderstanding will be corrected soon.
Since nosi (płaszcz) does not mean “he is wearing” it seems correct of Duolingo to reject such a translation.
What exactly are you proposing? That Duolingo teach us *ma na sobie," too? Or what do you mean by “this misunderstanding?” I think Jellei explained it all quite well in this thread.
There are two issues here. One refers to the use of the verb "nosić", which means regular, customary use of the coat only: "On (zawsze, zwykle, często) nosi płaszcz". If you look at the guy now and say he has the coat on now, as we speak, you say in Polish: "On ma (teraz, w tej chwili, w tym momencie) na sobie płaszcz".
The other issue has to do with the use of the Present Continuous aspect of the verb "to wear" by English speakers. To them, both sentences: "He wears a coat" and "He is (always) wearing a coat" have the same meaning, because the second sentence does not have to refer to the present moment, now. That is why, it would make sense if both sentences were accepted...