1)
What is the vengeance against the Goyim?
1.
Radak: They came to fight; we will take vengeance against them (Malbim - with a double-edged sword (6)), and kill all those who came to fight.
2)
What are "Tochachos"?
1.
Radak: The Goyim will argue with their kings why they came against [Yisrael]. Even so, they will not refrain from fighting against them.
2.
Malbim: Refer to 149:6:1:3.
3)
Is Le'umim the same as Goyim?
1.
Malbim: No. Le'umim have a common creed. They will come to argue about Emunah.