J.R.R. Tolkien created Sindarin as a Welsh-inspired Elvish language.
Sindarin is one of the major languages of Tolkien’s legendarium. In the fictional history of Middle-earth, it was spoken by many Elves of Beleriand and later became a common language among Elves in much of Middle-earth. Its sound and structure were especially influenced by Welsh.
Quenya is the other major Elvish language and was more strongly influenced by Finnish and Latin. That distinction is a frequent source of confusion: Sindarin is associated with Welsh, while Quenya is associated particularly with Finnish.
Tolkien was a philologist who designed languages with historical development, sound changes, and related vocabularies. Sindarin therefore appears not merely as a collection of invented words, but as part of a broader imagined linguistic history.