Albert Barnes Commentary 2 Kings 19:14

"And Hezekiah received the letter from the hand of the messengers, and read it; and Hezekiah went up unto the house of Jehovah, and spread it before Jehovah." — 2 Kings 19:14 (ASV)

Hezekiah received the letter - Inscriptions show that scribes accompanied the Assyrian armies with the materials of their craft, so that such a dispatch could be easily drawn up. Since Hezekiah himself “read” it, we may presume that it was in the Hebrew language.