“Once in a blue moon”in other languages

Same idea, different pictures

English has the blue moon, today taken to mean a second full moon in one calendar month. English and Afrikaans are also as scarce as hen's teeth, so skaars soos hoendertande: hens have no teeth at all.

Catholic countries count in deaths: every death of a pope in Italian, ogni morte di papa, every death of a bishop in Spanish, cada muerte de obispo. Spanish also says from Easter to Palm Sunday, de Pascuas a Ramos, almost a whole year, since Palm Sunday comes the week before Easter. Portuguese simply says de vez em nunca, from time to never.