When someone says “Bonsoir”, which means “Good evening” in French, the appropriate response is also “Bonsoir”. This is a polite and common way to acknowledge the greeting, especially in the evening or at night.
For example, if someone greets you with “Bonsoir”, you can simply reply with “Bonsoir” in return. This exchange is similar to saying “Good evening” and receiving the same greeting back in English.
In more casual settings, you might also hear people respond with “Salut” (Hi) or “Ça va?” (How are you?), but “Bonsoir” remains the most formal and appropriate response.