In an Italian book for beginners, I've seen that, to ask "What day is today?" in Italian, you may say "Quanti ne abbiamo oggi?". This seems an odd question to me since it looks as if we were asking "How many do we have today?". Could you please explain me this curious Italian expression in more detail?
It's an idiom, a standard phrasing Italian speakers don't even think about when using it, just like when asking in English for someone's age you apparently ask about them being more or less old, or when you stop working you “call it a day” (whom do you call a day? the day itself?).
Yes, the literal meaning would be “How many of them do we have today?”, “them” being presumably the days into the month, but it is now a stereotyped expression. On the other hand you could also, more transparently, ask: Che giorno è oggi? (but it's slightly more ambiguous, since you might be asking either about the date or the day within the week).
(Just to be pedant to a fault, you might ask “Quanti ne abbiamo oggi?” in other contexts too, where that ne [= “of them”] refers to something else. For instance, you might be talking about customers waiting for you, and ask a colleague “Quanti ne abbiamo oggi?” to mean literally “How many of them [= customers] do we have today?”.)
It's an idiom to ask the date, and it's a variation of the idiom "Quanto ne abbiamo oggi?" (using the singular).
While an Italian speaker will understand both and usually get that you're asking the date, replies might vary. eg:
- 15 Novembre
- 15 Novembre 2017
The version with "quanti" has more room to interpretation according to the context. So in a conversation like this
Alice: Oggi si gela! Bruno: Quanti ne abbiamo oggi? Alice: 15
Bruno is asking the temperature, not the date, and Alice gets that, providing the temperature in Celsius.
Other people prefers to ask "che giorno è oggi?" But that might either refer to the day of the week or of the month, and it's a 50/50 change to get the information you want. Today I prefer to answer with both and today I would reply "Mercoledì 15", but that's not the common answer.
If you want to avoid confusion, ask "che data è oggi?", that's the real meaning of that idiom.