Welsh strongly influenced the sound of Sindarin, J.R.R. Tolkien's Elvish language.
Tolkien developed Sindarin as one of the principal languages of the Elves in Middle-earth. Its phonology and general aesthetic were influenced especially by Welsh, while its historical development within the fiction was connected to the earlier language represented by Quenya.
Tolkien was a professional philologist who enjoyed constructing languages with internal histories, sound changes, and relationships between dialects. Sindarin was therefore not merely a collection of decorative words; it was part of a broader linguistic system used to give Middle-earth a sense of age and cultural depth.
Quenya is often confused with Sindarin because both are Elvish languages and both appear throughout Tolkien's mythology. Quenya has a different sound and was influenced in part by Finnish and Latin, while Sindarin's best-known real-world phonetic influence is Welsh.