The answer is supposed to be: "The boy says good day" but it doesn't sound correct. "Good morning" maybe, but "says hello" should be correct, no?
But "hello" is definitely less formal than "good morning" (even if not as informal as Polish "cześć")...
I'm not sure "Hello" is less formal than "good morning", it just doesn't mean the same thing. A less formal way would be "Hi"/"Hey" which would translate as "cześć" IMO. In any cases, it would be interesting to have an opinion of a native speaker for the sentence "The boy says good day" as it feels pretty old way to say things. Have a good day to you my dear, and see you on the morrow.
Maybe there are some sentences which accept "hello" for "dzień dobry", but we decided not to accept it.
To a large extent, English has dismantled its layers of formality in geetings. We can greet strangers at job interviews with "Hi" and it is not too informal anymore. To young people, "hey" is familiar, while "hi" feels more neutral. My students greet me, "Hey, sir." which seems an amusing mismatch of registers to me, but is normal to them. "Hello" works at any level of formality, but tends towards the formal nowadays. "Good day" is virtually a historical form now with very little current usage.
The situation is fluid. I wonder whether the acceptable translations could reflect this.
I agree that "good day" is archaic in American English. However, it is still common in other countries. The other translations, "good morning", "good afternoon" and "good evening" are quite common in the US. The suggested answer I was given was "good morning..."
Well, all is dependent on the exact sentence, but both may be correct translations.
How do I remember dzień dobry?? ive tried multiple things and none of them worked.
How about imagining that you have just met your brawny weightlifting neighbour and you are about to say good morning to him when you notice his rather fetching lilac eyeshadow. "gender, bro!" (dzień do-bry...)
It's tenuous but at least it's memorable.