"Have a nice day!"
I think this expression needs nunation to put it into the direct object case.
there is nunation in fact (yawmun) and I'm surprised to see a single correct audio on Duolingo Arabic.
The second word would come with nunation naturally, as it is an attributive adjective to (yawmun) but since it is the end of the phrase there is really no need to add the nunation to its end - it would be added if speech is to be continuous; e.g. يومٌ سعيدٌ يا أحمد (yawmun sa3ídun yá aHmad) (have a) nice day O Ahmad. Even with that, I can neglect the nunation on the second word if I remove (yá) and add a comma instead just to mark a stop in speech: يومٌ سعيد، أحمد (yawmun sa3íd, aHmad) (have a) nice day, Ahmad.
I failed to mention that it needs to be in حــالــة الــنــصــب or the accusative case, i.e. يومًا سعيدًا
And I agree there's no need to pronounce the complete nunation on the final word in the phrase, i.e. /yawman sa3ida/
There is no accusative case in the dialects, obviously, but in standard Arabic, it's required.
But I agree that there are lots of wrong answers involving tashkeel in these lessons.
Yep, the speech machine is not doing well at all. I would even say more than 50% of the audio recordings are wrong here.
Just to add, the other day I had some argument with someone here about the matching of names between Arabic grammatical conventions and the English (or Western ones in general).
In my opinion, حالة النصب simply means when the simple noun gets a (-a) to its end, but not necessarily being Accusative. Accusative by definition is the case of a noun being under the effect of the verb (or the verb acting on it) and typically this would be called مفعول به (done into). However, there are other cases, not related to the Accusative that still get the (-a) or (-an) to their endings and we still call it حالة نصب or the noun being Mansúb منصوب even though it is not accusative, like adverbs حال; Typically defined as a word describing the status of the verb. However, that other person argued and connected some endings which I don't remember trying to convince me that Adverbs are Accusatives as well and altogether they match the name النصب in Arabic. That doesn't make sense to me actually.
I've forgotten a lot of the grammatical terms but, yes, مفعول به is what this technically is. The complete sentence would be something like اتمنى لك يومًا سعيدًا i.e. 'I wish to you a good day', where 'a good day' is a direct object in English.