As we have seen many times before, many Italian expressions developed from Latin speech forms. The Italian idiom alle calende greche comes from the Latin phrase ad kalendas graecas and refers to the habit of delaying something indefinitely. More specifically, the expression refers to something that is perceived as extremely unlikely to happen or even impossible.
A fitting conceptual approximation for this expression can be found in the English idioms: in a month of Sundays and until doomsday. Also, more informally: when pigs fly and till hell freezes over.
A fitting conceptual approximation for this expression can be found in the English idioms: in a month of Sundays and until doomsday. Also, more informally: when pigs fly and till hell freezes over.