"Hello, I am a girl."
Translation:Bună, eu sunt o fată.
No. Buna and salut are like 'Hello' and 'Hi'. It doesn't matter who uses it. Buna means good for example buna dimineață, good morning. Salut is just like "Hello there" Romanian is a very confusing language even though it was the first language I learned. My parents are from Romania and I was born in America.
There is no significant difference. "Bună" is way more used and I think you can look at it as the short version of a more formal ”Bună ziua/seara” = ”Good afternoon/evening”. You can say it at any given moment. ”Salut”, with the longer option ”Salutare” is less frequently used, and it has the same level of formality, meaning you can easily say it to friends or people you say regularly, like colleagues. It is not really ok to say that for example in an interview or when you greet someone for the first time in a more formal environment.
It is neither correct nor necessarily used in regular, spoken terms. I think Duolingo disagreed because it is not a correct translation of their own sentence. Although in some cases you can skip the subject and ppl would understand you and it might even be correct and accepted, I think maybe in this case Duolingo disagreed because the translation was not complete. Maybe.