What is the name of the One Ring’s language in its inscription in J.R.R. Tolkien’s world?

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

The inscription begins with “Ash nazg durbatulûk,” meaning “One Ring to rule them all” in the Black Speech. Sauron created this language for the servants of Mordor, and the Ring’s verse uses it to express the central power relationship among the Rings of Power.

The complete inscription is written in Tengwar, the Elvish script, but the language itself is not Elvish. This distinction is a frequent source of confusion: writing system and spoken language are different things. The letters resemble an Elven script, while the words belong to the Black Speech.

The inscription appears when the Ring is heated, revealing fiery letters. Its full poem also mentions the Rings given to Elves, Dwarves, and Men, and identifies Sauron’s plan to control them through the One Ring.