Welsh inspired much of J.R.R. Tolkien’s fictional language Sindarin.
Sindarin is one of the principal Elvish languages in Tolkien’s mythology and is associated especially with the Sindar, or Grey-elves. Tolkien admired the sound and structure of Welsh, and its influence can be heard in many Sindarin words and names, including forms used for places and characters in Middle-earth.
Sindarin is not simply Welsh with invented vocabulary. Tolkien constructed it as part of a larger historical language family, giving it imagined sound changes and relationships to other Elvish tongues. Quenya, another major Elvish language, drew more strongly on Finnish and Latin influences. This distinction is a common source of confusion because both languages appear in The Lord of the Rings and The Silmarillion.