Phalera: The jewelry that holds the Holy Ecumune together.
There is no one language in the Covenant Empire. There are thousands. The client species and the guilds and the traders and the holy orders all speak their own tongues, and one cannot hope to learn them all. At one time, the common Sangheili language was the lingua franca of the whole empire. But languages shift, and they shift faster the further they are from the main trade routes. Nowadays, two individuals from far-flung corners of the Empire can both speak "Pan Sangheili", and be mutually unintelligible to each other.
Dai'neish Yll, the Liturgical Language, is the single exception, for it is a dead language. It is reserved solely for public worship throughout the Covenant Empire, for the communication of the clergy with their parishes, and is forbidden to use for mundane purposes. Not that many would want to. Dai'neish Yll is a language of poetry and imagery, steeped in ponderous tradition. Merely saying "hello" requires very formal use of metaphor. It is a fine language for the Covenant's top-down theocracy, but unsuitable for everyday use.
The translation disk was a necessary invention. The customs that grew up around them were inevitable in their own way. Many translation disks are embellished with elaborate designs to show the rank and station of a wearer, and are worn across the breast. When worn in this fashion, they are called phalera. Sometimes multiple phalera are worn, to complement an outfit or to demonstrate the many varieties of traveller that an official must deal with.
Because of the Covenant's edict against machine learning, translator disks built for general use are very limited machines. They can parse words within their internal dictionaries and construct sentences in accordance to the rules of grammar, but they cannot learn new words or new usages. This means that a phalera is locked to a group of dialects at a particular point in time, and as those languages change, the phalera must eventually be replaced. This also means that anyone speaking to an official with a slightly-out-of-date phalera must speak a version of their language that is formal and old fashioned to their ears, which generally suits the Sangheili just fine.