הֵ֛ן עֵ֥ד לְאוּמִּ֖ים נְתַתִּ֑יו נָגִ֥יד וּמְצַוֵּ֖ה לְאֻמִּֽים׃
Behold, I have given him for a witness to the peoples, A prince and commander to the peoples.
Rashi on Isaiah
a witness to nations A prince and a superior over them, and one who will reprove and testify of their ways to their faces. ([Mss., however, read:] One who reproaches them for their ways to their faces.)
Ibn Ezra on Isaiah
לאמים The people, the ל being radical; or to the people, the ל being a preposition.9There are in Hebrew two words which signify nation, namely: אֹם and לאֹם; pl. אֻמִּים (Ps. 117:1) and לאֻמִּים (49:1). For a witness. Messiah will testify, that there is no other king, no other ruler of the world, than God.