"Let's drink to his success."
Translation:Buvons à son succès.
Buvons-nous is definitely a question (Do we drink/Are we drinking). The imperative in French can be used with tu, vous and nous. In an imperative sentence, we use directly the verb, without using the subject at all. As there is no possible direct translation to English for the imperative conjugated with nous, we would translate it with the expression Let's. Basically:
- Bois à son succès! = Drink to his success! (informal singular you)
- Buvez à son succès! = Drink to his success! (formal or plural you)
- Buvons à son succès! = Let's drink to his success!