"Bună ziua" is not really good afternoon but more hello no ?
Literally "good day", but I've never heard someone use it to mean "Good afternoon." "Hello" or "Hi" should be an acceptable translation.
Good afternoon is the suggested one by Duolingo to be the best translation and as a secondary accepted translation is good day (even if this is not entirely the correct way of doing it).
Now I know I must have learned some Romanian as my subconscious is playing jokes on me. In revision exercise I now type 'Doulingo!'
The pronunciation of "bună ziua" is not the best one...The Duolingo's voice has a foreign accent...
Since when ziua is afternoon? the dictionary translates afternoon as: dupa amiaza. (Sorry for the missing accents)