Hi, why is it "Dzien dobry (Day good)" but "Dobranoc (Goodnight)"? (Why are the placements of the adjectives different? Is there a rule?
No rule in general. The thing with Polish is that the order of the words is not quite as important as in English, so just watch for that.
In a lot of European languages, including Spanish, you often have the noun and verb in a different order. So "bus czarny" would translate into "the black bus" instead of "the bus black". But if you were speaking native Polish, you'd be saying it "backwards" ("bus czarny") and it would be grammatically correct, it wouldn't sound "wrong" to you like it does now.
Also, I think that "dobranoc" cheats because it's a single world and so the reversing rule of thumb doesn't apply. But I'm not fluent in Polish so perhaps someone can give a better explanation.
Becasue of convetion/tradition: "Dobranoc", but "Dobry wieczór" (= "Good evening"), but "Dzień dobry"... (see also EmicciLucksy's question and Baakamono's comment).
Ah, the inconsistencies of language: Good morning, good afternoon, good-bye, good night, and even goodnight.
Italians seem to be consistent: buongiorno, buonasera (bonanotte). French: bonjour, bonsoir, bon nuit. Oh well ................
It should be Dobra noc but people have been using dobranoc for some time now. Both are acceptable.
Compare with Italian "Buongiorno" or French "Bonjour" which are also written as one word.
Is "Good night" in Polish the same as English in that it's a parting phrase and never a greeting?
Yes, a good-bye, not a hello. Dobry wieczór is used as a hello, "good evening."
We don't write it that way, unless we literally mean "a good night". So while I can understand why you think that, it would in my opinion do more harm than good to accept it.
Is it dumb of me to learn Polish in English although my native laguage is Dutch? Cuz i feel like I'm better at English than at Dutch tbh XD
Most people taking this course aren't native speakers of English, and there isn't any course of Polish for speakers of other languages here.
For the future: if you won't tell us what your answer was, we will not be able to find out why was it rejected and if it's really wrong.