J.R.R. Tolkien based the invented language Quenya mainly on Finnish.
Tolkien was a professional philologist, and he designed his fictional languages with detailed sound systems, grammar, and histories. Finnish particularly influenced Quenya’s structure and vocabulary, while Welsh strongly influenced the sound and style of another major Elvish language, Sindarin.
Quenya is presented in Tolkien’s mythology as an ancient, formal language of the Elves. Its name is often translated as “speech” or connected with the idea of speaking, and it functions in the stories somewhat like a learned or ceremonial language.
Finnish was an inspiration rather than a direct source for every Quenya word. Tolkien transformed his influences into an original language family with its own internal development. This is why Quenya can resemble Finnish in places without being Finnish vocabulary written in a fantasy setting.