Traduction :Bonne nuit.
To sum up :
"Bonne nuit", (meaning, you're going to sleep, nothing else planned) = good night
"Bonsoir", (starting when sundown, approximately) = good evening
"Bonne soirée", (you're leaving a place, during evening, but others stay and carry on) = Have a nice evening
However, "Bonsoir", is quite used when you're in a formal situation, as you could be during an official event or at a place you are not familiar with the people. So, at anytime, you would use "Bonsoir", starting on your arrival up to your departure from this place (on the evening obviously). But, you will not be blamed if using "Bonne nuit" ;)
Bonsoir = en un mot.
Que penses-tu Allintolearning à propos de good night et goodnight? C'est comme "good bye": on le trouve mais certaines personnes le considère comme incorrect?
En français, si c'est 3 heures du matin, tu diras plutôt bonne nuit que bonsoir!