J.R.R. Tolkien created Quenya before Sindarin.
Quenya is one of Tolkien’s principal Elvish languages and is strongly influenced by the sound and structure of Finnish, as well as by elements of Latin and Greek. Tolkien began developing its earliest forms during the 1910s, before the mythology of Middle-earth had reached its final shape.
Sindarin developed later from an earlier language Tolkien called Goldogrin or Gnomish, which was influenced chiefly by Welsh. Tolkien designed relationships between his languages as if they had evolved historically, so Quenya and Sindarin are related but have different sounds, vocabulary, and cultural roles.
Quenya became associated with the High Elves and with formal or ceremonial speech. Sindarin became the everyday Elvish language of many Elves in Middle-earth, especially in Beleriand and later in regions such as Lindon and Lothlórien. The distinction can be obscured because Tolkien repeatedly revised both languages and their histories. Quenya was developed first, but its fictional chronology is not the same as the chronology of Tolkien’s real-world work on it.