What language did J.R.R. Tolkien invent for the inscription on the One Ring?

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

The inscription begins, “Ash nazg durbatulûk,” translated as “One Ring to rule them all.” Tolkien created the Black Speech for Sauron and the servants of Mordor. The Ring’s words are a compact statement of domination, linking the Rings of Power to Sauron’s purpose.

Quenya and Sindarin are Elvish languages, while Westron is the Common Speech used by many peoples in The Lord of the Rings. Those languages are closely associated with Tolkien’s world but are not the inscription’s language. The Ring’s letters are written in Tengwar, an Elvish writing system, which can cause another confusion: the script and the language are different. Tolkien supplied the inscription in the chapter “The Shadow of the Past.”