cold day in Hell

English

cold day in Hell (plural cold days in Hell)

(idiomatic, slang) The time of occurrence of an event that will never happen.
It'll be a cold day in hell when that happens.

an event that will never happen

Basque: haizerik ez den urtean (in the year without wind)
Belarusian: калі рак свісне (kali rak svisnje)
Bulgarian: когато цъфнат налъмите (kogáto cǎfnat nalǎmite) (when pattens blossom)
Chinese:
Mandarin: 绝不可能, 绝无可能
Danish: en kold dag i helvede
Dutch: met Sint Juttemis; als pasen en pinksteren op één dag vallen
Esperanto: triĵaŭda semajno (week with three Thursdays)
Finnish: kun helvetti jäätyy (when Hell freezes over)
French: quand les poules auront des dents (fr) (when hens will have teeth), semaine aux quatre jeudis (fr) (week with four Thursdays)

German: nie im Leben (not in a lifetime)
Greek: όταν ασπρίσει ο κόρακας και γίνει περιστέρι (ótan asprísei o kórakas kai gínei peristéri)
Hungarian: majd ha piros hó esik (when red snowflakes are snowing), majd ha cigánygyerekek potyognak az égből (when gypsy children are streaming from the sky), majd ha a pokol befagy (when Hell freezes over)
Italian: alle calende greche (when it will be a Roman holiday in the greek calendar), quando gli asini voleranno (when donkeys will fly), mai (it), quando gli asini voleranno
Persian: وقت گل نی‎‎
Polish: jak rak świśnie a ryba piśnie (pl)
Russian: когда́ рак на горе́ сви́стнет (ru) (kogdá rak na goré svístnet) (when a crayfish whistles on the mountain), по́сле до́ждичка в четве́рг (ru) (pósle dóždička v četvérg) (after a small rain on Thursday)
Spanish: cuando las ranas críen pelo (es), cuando meen las gallinas
Turkish: kırmızı kar yağınca (when it snows red), çıkmaz ayın son çarşambası (tr) (the last Wednesday of the non-ending month)