Finnish most strongly influenced J.R.R. Tolkien’s Quenya.
Quenya is one of Tolkien’s constructed languages for the Elves. He admired the sound and structure of Finnish, and Finnish grammar helped inspire Quenya’s form, especially its rich case system and distinctive phonology.
Tolkien also drew on other languages. Welsh was especially important to Sindarin, while Latin and Greek contributed influences elsewhere in his linguistic imagination. Quenya is not Finnish with invented vocabulary; it is an original language with its own history, grammar, and relationship to the fictional languages of Middle-earth.