Which language did Tolkien invent for the Elves of Doriath?

Tolkien invented Sindarin for the Elves of Doriath. In the linguistic history of Middle-earth, Sindarin developed from the language of the Sindar, or Grey Elves, who lived in Beleriand during the First Age.

Doriath was the woodland realm ruled by Thingol and Melian. The Sindarin language used there became the most widely spoken Elvish language among the Elves of Middle-earth in the later First Age and the subsequent periods depicted in Tolkien’s stories.

Quenya is another major Elvish language, but it was associated primarily with the High Elves who came from Aman. Tolkien modeled aspects of Sindarin’s sound and historical development on Welsh, while Quenya drew strongly on Finnish and other linguistic influences.

The names of many places and people in The Lord of the Rings are Sindarin. “Mithrandir,” “Rivendell,” and “Lothlórien” are examples of names connected with Tolkien’s Elvish linguistic system, though individual names can have complex histories.