Sindarin is the Tolkien language spoken by many Elves of Rivendell and Lothlórien.
Tolkien based Sindarin’s sound and historical development largely on Welsh. In the languages of Middle-earth, it becomes the commonly used Elvish language among many Sindar and later among other Elves in Middle-earth. Characters such as Elrond, Arwen, and Legolas are associated with Sindarin names or speech.
Quenya is another major Elvish language, but it functions more like a formal or scholarly language in much of the Third Age. Tolkien modeled Quenya chiefly on Finnish and gave it an older, prestigious status among the Elves. Sindarin and Quenya are therefore related but not interchangeable. Khuzdul is the secret language of the Dwarves, while the Black Speech is associated with Sauron and Mordor. Spellings and pronunciation can vary in popular adaptations, but Sindarin remains the standard answer for the commonly spoken Elvish language in the late histories.