J.R.R. Tolkien based much of his constructed language Quenya on Finnish.
Quenya is one of Tolkien’s Elvish languages and is associated especially with the High Elves. Its sound patterns and grammar were strongly influenced by Finnish, while its vocabulary and history were developed as part of Tolkien’s own mythology. Tolkien also drew on other languages, including Latin and Greek, when shaping his linguistic creations.
Within the fictional history of Middle-earth, Quenya originated as the language of the Elves of Valinor. It later became a language of learning and ceremony in parts of Middle-earth rather than the everyday speech of most Elves there.
Sindarin is a separate major Elvish language, more widely used in Middle-earth and influenced in its design by Welsh. The two are sometimes confused because both appear in Tolkien’s legendarium, but they have different fictional histories and linguistic inspirations. Tolkien’s language invention was central to his world-building, not merely a method for naming characters.