The Elvish language spoken by many Sindar in J.R.R. Tolkien’s legendarium is Sindarin.
Sindarin is one of Tolkien’s most developed Elvish languages. It is associated especially with the Sindar, or Grey-elves, who remained in Middle-earth rather than completing the journey to Valinor. In the First Age, Sindarin became the everyday language of many Elves in Beleriand and influenced the naming traditions encountered in later stories.
Tolkien based much of Sindarin’s sound and historical development on Welsh. The language has its own grammar, vocabulary, and sound changes, rather than being a collection of invented names. Readers encounter Sindarin-derived names such as Aragorn, Legolas, and Minas Tirith throughout The Lord of the Rings, although the texts also contain names from other languages.
Sindarin is often confused with Quenya. Quenya is another major Elvish language, associated more strongly with the High Elves and influenced by Finnish. Khuzdul is the secret language of the Dwarves, while Adûnaic was spoken by the Númenóreans. These languages occupy different cultural and historical positions in Tolkien’s world.