Sindarin is the fictional Elvish language most influenced by Welsh in J.R.R. Tolkien’s legendarium.
Tolkien based many of Sindarin’s phonological features and overall feel on Welsh, a language he admired. Sindarin became the everyday Elvish language of many Elves in Middle-earth, especially in the later history of the First and Second Ages and during the events of The Lord of the Rings.
Quenya was another major Elvish language, but Tolkien associated its design more strongly with Finnish and Latin. The two languages are related within Tolkien’s invented linguistic history and descend from an earlier tongue called Common Eldarin.
Sindarin appears in names such as Galadriel, Celeborn, and Minas Tirith. Tolkien’s detailed language construction is one reason his fictional cultures feel historically layered rather than merely decorated with invented words.