en_tn/deu/32/08.md

gave the nations their inheritance

This is an idiom. "put the nations in the places where they would live." Similar words, "giving to you as an inheritance," appear in Deuteronomy 4:21. (See: rc://en/ta/man/jit/figs-idiom)

according to the number of the children of Israel

God has arranged the nations according to the way they relate to Israel.

the number of the children of Israel

How this relates to "the boundaries of the people" is not clear. Some ancient and modern translations read, "the number of the angels of God" or "the number of the children of God." That is, God assigned an angel to each other nation, but he rules Israel directly.