Which fictional language is used for the inscription on the One Ring in J.R.R. Tolkien’s lore?

The inscription on the One Ring is written in the Black Speech of Mordor.

The Ring bears the verse beginning “Ash nazg durbatulûk,” which translates into English as “One Ring to rule them all.” Tolkien describes the Black Speech as a language created by Sauron for the servants of Mordor. The inscription was made using Tengwar letters, but the script and the language are different things.

This distinction causes a common mix-up. Tengwar is a writing system, while Black Speech is the language represented by the Ring’s inscription. Quenya and Sindarin are Elvish languages, and Khuzdul is the language of the Dwarves. The Ring verse also appears in the longer poem that links the One Ring with the Rings of Power made for Elves, Dwarves, and Men.