In general this isn’t going to work with any language that the people reviewing the recording can find a translator for, however a variant of the idea did serve the Allies in WWII. Native Americans were drafted into the military as “code talkers”. They used their native languages to send and receive radio messages, and, as the Axis powers did not have access to anyone who spoke those languages, they could not understand intercepted messages.

Although no code talkers was ever captured, it is alledged that a member of each unit they were attached to was given a secret duty to shoot them if it looked like they would be, in order to protect the code.