Jeremiah 5:15

Israel is not put here for the ten tribes, but for the whole house of Jacob, of which Judah was now the representative.

Mighty - “permanent, enduring.” The word is the usual epithet of the rocks Numbers 24:21, and of ever-flowing streams Deuteronomy 21:4, Hebrew). It describes therefore a nation, whose empire is firm as a rock, and ever rolling onward like a mighty river. The epithet “ancient” refers simply to time.

Whose laguage thou knowest not - This would render them more pitiless, as they would not understand their cries for mercy.