Where does “Japon” come from?

Japon (English) comes from Latin Iaponia, from Latin -ia, from Latin -ius, from Proto-Italic -jōs, from Proto-Indo-European -yós — Creates adjectives from noun or verb stems.

Ancestry of “Japon”, step by step

Japon traces back through two separate lines of ancestry.

via Latin Iaponia

Step	Language	Word	Meaning
1	Latin	Iaponia	Japan
2	Latin	-ia	Used to form a feminine abstract noun, usually...
3	Latin	-ius	forming adjectives from nouns; nominative neuter...
4	Proto-Italic	-jōs	Forms comparative adjectives
5	Proto-Indo-European	-yós	Creates adjectives from noun or verb stems

via French japon

Step	Language	Word	Meaning
1	French	japon	japanware; Japanese porcelain
2	Portuguese	Japão	Japanese
3	Malay	Jepang	Japanese
4	Hokkien	日本	Japan; Japanese; Japan
5	Middle Chinese	日本	Land of the Rising Sun

Every word from Proto-Indo-European -yós →Every word from Latin -ia →Every word from Latin -ius →