(the ring-inscription is said to be written in the Black Speech, a language devised by Sauron and used in his land of Mordor. It is written in tengwar.)
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The Tengwar[1] are an artificial script created by J. R. R. Tolkien. In his fictional universe of Middle-earth, the tengwar were invented by the Elf Fëanor, and used first to write the Elven tongues: Quenya, Telerin, and also Valarin. Later a great number of languages of Middle-earth were written using the tengwar, including Sindarin. Tolkien used tengwar to write English: most of Tolkien's tengwar samples are actually in English.
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Ash nazg durbatulûk, ash nazg gimbatul,
Ash nazg thrakatulûk agh burzum-ishi krimpatul.
Translated, the words mean:
One ring to rule them all, one ring to find them,
One ring to bring them all and in the darkness bind them.