From Halopedia, the Halo wiki
A translation disk (disc) or translator disk is a piece of technology used for translating spoken words to other languages.
Translator disks use translation software to detect spoken words and then repeat them in another desired language so that individuals may speak that otherwise would be unable to. These disks can be programmed with the capacity to understand and translate languages from multiple species. The translated speech has an electronic undertone to it and can sound somewhat distorted. Translation disks can be easily deactivated and reactivated and may be hung around a user's neck or secured high on one's breastplate.
History of use
Translation disks were used by the Covenant and after its downfall they continued to be employed by Jiralhanae in the Keepers of the One Freedom. Notably, Castor, a leading dokab of the Keepers, kept one around his neck. Orsun, his second-in-command, did likewise.
List of appearances