J.R.R. Tolkien created Sindarin as an Elvish language influenced partly by Welsh.
Sindarin is one of Tolkien’s best-developed fictional languages and is spoken by many Elves in Middle-earth. Tolkien modeled much of its sound and structure on Welsh, one of the real-world languages he admired. He also gave Sindarin a historical relationship to Quenya within the fictional history of the Elves.
In Tolkien’s internal chronology, Sindarin developed from Common Telerin among the Elves who remained in Middle-earth. It became the everyday Elvish language of many Sindar and was widely used in the western regions of Middle-earth during the events of The Lord of the Rings.
Sindarin is often confused with Quenya. Quenya was another major Elvish language, influenced especially by Finnish and associated with the High Elves. Khuzdul was the secret language of the Dwarves, while the Black Speech was created by Sauron for his servants.