Which language is the inscription on the One Ring written in, according to J.R.R. Tolkien’s Middle-earth legendarium?

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

The fiery inscription begins, “Ash nazg durbatulûk,” and continues with the lines translated as “One Ring to rule them all, One Ring to find them.” The verse is part of a longer rhyme describing the Rings of Power and the One Ring’s domination over them.

Tolkien created the Black Speech for Sauron and associated it with Mordor. The inscription is not written in Quenya, the High-elven language, or Sindarin, the language widely used by Elves in Middle-earth. Khuzdul is the secret language of the Dwarves and is also unrelated.

The Ring’s writing appears only when it is heated, revealing its letters in fire. In Tolkien’s story, the inscription provides a direct linguistic and visual link between the Ring and Sauron’s attempt to control the other Rings of Power.