Why did all the Goyim gather?
Rashi: If they would all gather, who among them and their Nevi'im will tell future events or similar matters based on their idols?
Radak: Past tense is used in place of future. They and all their Chachamim will gather.
What is "Yagid Zos"?
Radak: It is this that will be in the future.
Malbim: After the Nevu'ah of the gathering of exiles, he turns to the idolaters of his time, who told wonders of their idols. Greek mythology is the remnant of those follies. Do they tell anything famous that encompasses the entire world, like the gathering of exiles?! They tell only about the past that no living person remembers.
What is the meaning of "v'Rishonos Yashmi'unu"?
Rashi: Matters that already passed - will they say, we told them before they came?!
Radak: It is Sancheriv. Did they tell us before they happened, like I told you via a Navi?!
Malbim: The idolaters only tell matters of the past.
What is the meaning of "Yitenu Edeihem v'Yitzdaku"?
Rashi: Let them bring witnesses who heard their Nevu'ah before it was fulfilled, and they will be justified. Radak - we will say that they were correct and faithful in their words.
Malbim: One who tell a wonder of the past, he must verify his words via witnesses who saw it, or it must be logical and the listener understands that it is Emes - "v'Yishme'u v'Yomeru Emes."
Why does it say "v'Yishme'u v'Yomeru Emes"?
Radak: If they will not know, they will hear what the Navi says, and say that it is Emes; they will admit to the Emes.
