Finnish was a major inspiration for the sound and structure of J.R.R. Tolkien's invented language Quenya. Tolkien admired the language's appearance and grammar, and Finnish helped inspire the linguistic design of the language associated with the Elves of Valinor.
Quenya is not Finnish with altered vocabulary. Tolkien constructed it as an independent language, drawing on several linguistic influences and developing its own history, sounds, grammar, and vocabulary. He also connected Quenya to fictional earlier forms within the history of the Elvish languages.
Welsh was especially important to the sound and development of Sindarin, another major Elvish language. Latin and Gothic influenced Tolkien's scholarly interests and some aspects of his invented languages, but they are not the standard answer to the question about Quenya's strongest real-world inspiration.