Translation:A Japanese airline
I think these are the correct translations: 일본 항공사 → Japanese airline 일본의 항공사 → Japan's airline.
Japan has more than one airline. The possessive includes the properties of the definite article, as do numbers and such, IMHO. So I'd add an s: (one of) Japan's airlines, but they're effectively indistinguishable from Japanese airlines in English AFAIK.