The word "he" refers to Jephthah and all the fighting men of Gilead. Alternate translation: "they fought against Ephraim" (See: [[rc://en/ta/man/translate/figs-synecdoche]])
You can make the meaning of this insult explicit. Alternate translation: "You Gileadites do not really belong here. You are just people who came here to live" (See: [[rc://en/ta/man/translate/figs-explicit]])
"in the regions of Ephraim and Manasseh" or "in the land of Ephraim and Manasseh." Here "Ephraim" and "Manasseh" refer to regions and are named after the tribes which live there.