Welsh strongly influenced the sound of J.R.R. Tolkien’s Sindarin.
Sindarin is one of Tolkien’s principal Elvish languages and is spoken by many Elves of Middle-earth. Tolkien drew inspiration from the phonology and appearance of Welsh while constructing it, creating a language with consonant mutations and a sound pattern that recalls Welsh without being Welsh itself.
In Tolkien’s internal history, Sindarin developed from an earlier Elvish language and became especially prominent among the Sindar, or Grey-elves. It is the source of many familiar names, including Minas Tirith and Lothlórien, though Tolkien’s linguistic histories can involve several stages and dialects.
Quenya, the other best-known Elvish language, was influenced strongly by Finnish. The two languages are not simply formal and informal versions of one another; they have different histories, sounds and cultural associations within Tolkien’s mythology.