en_tn/jdg/11/11.md

leader and commander

These two words basically have the same meaning repeated to emphasize how important Jephthah had became. You can combine the two words. AT: "commander" (See: rc://en/ta/man/translate/figs-doublet)

When he was before Yahweh in Mizpah, Jephthah repeated all the promises he made

This is an idiom. Here the phrase "before Yahwheh" means that he repeated his promises as a vow before Yahweh. AT: "When Jephthah was in Mizpah he repeated all of these promises as a vow before Yahweh" (See: rc://en/ta/man/translate/figs-idiom)

all the promises he made

This refers to the promises he made to the leaders of Gilead about becoming their leader.