“When pigs fly”in other languages

Same idea, different pictures

Every language picks something impossible. Pigs fly and hell freezes over in English, hens grow teeth in French, quand les poules auront des dents, a crayfish whistles on a mountain in Russian, and a cow coughs in Brazilian Portuguese, nem que a vaca tussa.

Some pick a date that never comes. French and Italian say on the Greek calends, aux calendes grecques, alle calende greche: the calends were the first day of the Roman month, when debts fell due, and the Greek calendar had none. The emperor Augustus is said to have used it for debtors who would never pay. French also waits for Saint Glinglin's day; there is no such saint. Russian waits until after the little rain on Thursday, после дождичка в четверг.