Speak … unto thy servants in the Syrian language; literally, in the Aramaic language. Aramaeans were widely spread over the entire region between the Lower Tigris and the Mediterranean; and their language seems to have been in general use, as a language of commerce.
"Private contract tablets in Aramaic and Assyrian have been found in the remains of ancient Nineveh" (Cheyne). Rabshakeh had, perhaps, spoken "in the Jews' language " without any ill intent, thinking that it was the only tongue which Jewish envoys would understand; but his so doing was calculated to affect the minds of the common people, and to shake their allegiance to Hezekiah.
The envoys, therefore, requested him to employ a foreign tongue, and suggested Aramaic as one which was familiar to them, and which they supposed that he would understand. His employment of Hebrew had shown them that he was a linguist.
In the Jews' language. There was no language peculiar to the Jews as Jews, that is to say, different from the ordinary speech of the Israelites. Both alike spoke Hebrew. In the Old Testament, however, this corn-men language is never called "Hebrew," but either "the tongue of Canaan" (Isaiah 19:18) or "the Jewish language" (2 Kings 18:26, 2 Kings 18:28; 2 Chronicles 32:18; Nehemiah 13:24).
Similarly, our own tongue is called "English," though spoken also in Scotland, Wales, Ireland, America, and Australia. In the ears of the people that are on the wall; i.e. of the soldiers placed on the wall to defend it.
We must suppose that the conference took place immediately outside the fortifications, so that some of those on the wall could hear.