Translation:Twenty-one ducks and a first apple
Papa Duck: You know, little duck, you will be considered grown-up when you with your twenty friends will eat the first apple of your lives. This is our tradition. But you are too young for that.
Little Duck: Look! A gathering is taking place at the town hall! Look at the young ducks in the center! And what's there on the table? Why, it's an apple of course! Twenty-ducks and a first apple!
Of course not, but it's a clever way to use this "bug" to test your vocabulary and attention level.
At first, I was tempted to write "the first apple", which is the correct form, but yeah, these sentences are randomly made, and it is bound that at some point something isn't grammatically correct.
I can't think of a situation in which I would use "a first" to descrive anything. Even something like "a first child" or "a first son" feels clumsy and incorrect. I think it's because the "a" and the "first" both carry similar meanings. "The first", on the other hand, makes perfect sense. It just wouldn't be alliterative.
"A first X" sounds natural to me (U.S. English speaker) in some contexts -- "A first date can be an awkward experience," for example, sounds fine, and implies that there will be multiple first dates with different people; if I were talking about someone's first date with a specific person, then I'd use "The first date". "A first child" sounds weird because I'm expecting "A first-born child".
I agree, I hadn't thought of "a first date". Although maybe it's because (as a native British English speaker) we don't tend to refer to dates, but more to "going out with someone". I wonder if the majority of "a first" phrases seem more nature as they are more like set phrases, as opposed to "a first apple". I'm not sure whether you could refer to them as noun phrases.
In Mandarin we say "Hei huafei huifa bian hui huafei" （黑化肥挥发变灰化肥, which literally means "black fertilizer becomes gray fertilizer after volatilization“）. Besides the tongue twisters, there are some sentences that look symmetrical. “上海自来水来自海上，山西悬空寺空悬西山" （shang hai zi lai shui lai zi hai shang, shan xi xuan kong si kong xuan xi shan），meaning: the tap water for Shanghai comes from the sea, the hanging temple of Shanxi Province hangs on the west hill. :D
To make the distinction between 'een' meaning 'one' and 'een' meaning 'a(n)', 'een' meaning 'one' gets the accents: 'één'. In 'eenentwintig' or 'eenendertig' the meaning is always clear. They don't get accents (unless maybe you want to stress 'éénentwintig' as opposed to 'tweeëntwintig').
This is just a fun nonsense sentence in which every word except the last one starts with an "e." Like the tongue twister "She sells seashells by the seashore." I mean who the hell sells seashells, especially near a seashore? Not much of a demand for them in real life, I imagine. Not too hung up on what "first apple" means or how to translate it.
I'm going to suggest :"Twenty one ducks and a single apple." The alliteration in Dutch is great--loved it! But to translate it into English as "a first apple" makes the sentence rather inane. A single apple is cute, but presents a dilemma for the person with the apple, especially if the ducks are aggressive ones.