Which language family did J.R.R. Tolkien’s invented language Sindarin belong to?

Tolkien’s invented language Sindarin belonged to his Elvish languages. In the fictional history of Middle-earth, Sindarin was the language of the Sindar, or Grey Elves, and became widely used among Elves in Beleriand and later regions.

Tolkien designed Sindarin as part of a related family of Elvish languages. Its historical development within the legendarium is connected to earlier forms such as Common Telerin and the language of the Teleri. The sound and structure of Sindarin were influenced especially by Welsh, while Quenya was influenced strongly by Finnish and Latin.

Sindarin is often called simply an “Elvish language,” but Tolkien created multiple Elvish tongues with different histories and functions. Quenya and Sindarin are the two most prominent in The Lord of the Rings, and they are not interchangeable names for one language.