Paese che vai, usanza che trovi
Literally: Whatever country you go to, you'll find its own custom
What it really means
When in Rome, do as the Romans do — respect local ways.
When nonna would say it
Said to encourage open-mindedness when travelling, or to explain why things are simply done differently elsewhere.
Picture this
You're baffled that the shops all shut for three hours at lunch. Nonna spreads her hands philosophically: «Paese che vai, usanza che trovi.»