What were the two major Elvish languages created by J.R.R. Tolkien for The Lord of the Rings?

The two major Elvish languages created by J.R.R. Tolkien for The Lord of the Rings were Quenya and Sindarin.

Quenya and Sindarin are the best-developed and most prominent Elvish languages in Tolkien’s Middle-earth writings. Quenya is associated especially with the High Elves and draws inspiration from the sound and structure of Finnish, while Sindarin is the commonly spoken Elvish language of many Elves in Middle-earth and was influenced in part by Welsh.

Tolkien was a professional philologist who developed languages with grammar, vocabulary, sound patterns, and historical relationships. He did not invent isolated lists of fantasy words; he imagined languages changing over time and belonging to communities with distinct histories.

Other languages appear in the legendarium, including Dwarvish Khuzdul, the Black Speech of Mordor, and the human language Adûnaic. Those names are therefore not alternatives to the two principal Elvish languages asked for here.