cosmopolis
A city inhabited by people from many different countries and cultures; a cosmopolitan city. Used in academic or literary contexts.
New York is truly a cosmopolis.
国際都市 is a more common Japanese term for 'international city', while コスモポリス is a rarer, more literary loanword emphasizing cultural diversity.
Borrowed from English 'cosmopolis', ultimately from Greek 'kosmos' (world) + 'polis' (city).