Med-wah

Med-wah is an Egyptian Divine Word that can be used to communicate between two or more different languages by turning the foreign language(s) into Ancient Egyptian, but everyone around hears it as if it was their mother language. This spell has been used by Iskandar and Amos Kane.

The Red Pyramid
Iskandar implicitly uses this spell when he first meets Carter and Sadie Kane. He speaks in his native tongue, Alexandrian Greek, while Carter and Sadie speak in English. Due to the spell, they understand each other. Iskandar later hints to Sadie that he isn't actually talking in English.

The Serpent's Shadow
Leonid escapes from Russia to the First Nome to meet the magicians fighting Apophis. Since he speaks only Russian and the other magicians don't understand Russian, Amos uses this spell so that they all can communicate. He later explains how the spell works.