J.R.R. Tolkien created Quenya, a fictional language shaped by Finnish, Latin, and Greek influences.
Quenya is one of the major Elvish languages in Tolkien's mythology. He developed it as a historical language with its own sounds, grammar, vocabulary, and changes over time, rather than as a random collection of fantasy words. Finnish was especially important to its sound and structure, while Latin and Greek contributed additional inspiration.
Within the stories, Quenya is associated particularly with the High Elves and is often treated as a formal or ancient language. Sindarin, another major Elvish language, became more commonly spoken in much of Middle-earth during the Third Age. The two languages are related in Tolkien's invented linguistic history but are not interchangeable.
Tolkien's professional study of languages strongly influenced his fiction. In fact, his world-building often began with language history and then expanded into peoples, places, legends, and texts.