The Ring inscription in J.R.R. Tolkien’s legendarium is written in the Black Speech of Mordor.
The inscription appears on the One Ring when it is heated, revealing fiery writing in the language created by Sauron. Its words begin, “Ash nazg durbatulûk,” commonly translated as “One Ring to rule them all.” The verse links the Ring to the other Rings of Power and states Sauron’s purpose in making it.
Tolkien designed the Black Speech as a language associated with Sauron and the servants of Mordor. It is deliberately distinct from the Elvish languages that receive much more extensive treatment in his linguistic work. The Ring’s writing uses Tengwar characters, but the script and the language are separate matters.
A frequent confusion is to call the inscription an Elvish language because it uses elegant lettering. Tengwar is the writing system; Black Speech is the language represented by the words on the Ring.