Jewish thought teaches that every nation has a particular goal or purpose set for it by God.

Really? I've never heard that before. I've heard the "Other Prophets" thing, but I hadn't heard the idea that every nation had some specific purpose.

May I ask - When you say "Nation" here, do you mean peoples or do you mean something more in line with modern Nation-States?

For example - Would this "purpose" be connected to say... the Celtic people or the Han people or the Turks or what have you?

Or is it more like America as a nation has a purpose. South Africa as a nation has a purpose. Etc.

If it is more of a "People as a nation" thing... Does this purpose evolve with time? Or is it some sort of Cosmic Clockwork where everything has a more timeless place in the greater scheme of things?

Take Northern Europeans. In antiquity one might well have assumed our "purpose" involved humbling big headed empires (Teutoburg forest and the like) though over time we've essentially evolved into said big headed empire.

Or would the "purpose" being something more abstract/complex than that?

Other prophets outside the Jewish canon may have existed and taught other nations. God may have had conversation with other peoples.

I'm curious. Is there any leeway given to local spiritual traditions in this regard, or is it assumed that there are simply named prophets, forgotten to history, who were more or less like the Abrahamic Prophets and that local traditions are sinful in some capacity?

Am I putting to much thought into this?

It's just the element of Abrahamic Faith I find myself the most curious about. The view of other peoples and their connection/relationship to the God of Abraham.