Where does “Kongolese” come from?

Kongolese (German) comes from German -ese, from English -ese, from Middle English -eys, from Old French -eis, from Late Latin -iscus.

Kongolese (German): Congolese

Definitions

Step	Language	Word	Meaning
1	German	-ese	Forms nouns indicating an inhabitant of a place
2	English	-ese	Used to form adjectives and nouns describing...
3	Middle English	-eys	Alternative form of -esse
4	Old French	-eis	used to form nationalities; used to form names of...
5	Late Latin	-iscus	—