The Emperor's Royal Guard battle language was a language understood only by the Emperor's Royal Guard.
Due to the fact only Guardsmen understood it, it was fool-proof when sent on a comlink, as even if the Rebels decrypted the frequency, they couldn't find any phrase on any available database. Even Palpatine and Darth Vader didn't understand it. After the majority of the Guard was eliminated, Kir Kanos used the version of his name in the language, Kenix Kil, as an alias.
Tav Kennede was the only known non-guardsmen who knew the language.