"Hello, good morning!"
Translation:Xin chào, chào buổi sáng!
Why wouldn't "Xin chào, buổi sáng" be accepted. The question wasn't "Hello, hello good morning."
Xin chào , buổi sáng means Hello, morning ! Well, good morning actually means buổi sáng tốt lành.
Where do you see the hint "chúc buổi sáng tốt lành"? For this phrase, "chúc buổi sáng tốt lành", it is very old and classy. You are recommended not to use it in verbal or writing form.
Your question refers to a complicated issue in the use of languages. In Vietnamese, grammatically, your suggestion "chúc buổi sáng tốt" would make perfect sense. Same with "good day" - "ngày tốt". However Vietnamese language is influenced by people's preference rather than following grammar book. I would argue that long ago (maybe before the Wars), some guy wrote a book, a play or any kind of Vietnamese-based work, he/she used "buổi sáng tốt lành" in his/her work instead of "buổi sáng tốt". ("tốt lành" is simply an emphasized version of "tốt", with "lành" being "no bad thing occurred"). And guess what, people sticked to it. Thus, the phrase becomes "standard" without explanation and "buổi sáng tốt" sounds very wrong for no reason.
In short, let's try not to say "good morning" in Vietnamese when you attempt to start a conversation.