The language of the Grey-elves of Beleriand and most commonly used of the Elf-tongues in Middle-earth. When the Noldor returned to Middle-earth at the beginning of the First Age, Thingol decreed that their tongue, Quenya, was not to be spoken in his realms. So the language of his people, Sindarin, came to dominate. Quenya, though, was still used as a language of ceremony and poetry.

Sindarin shared common roots with Quenya, and the two languages had many similar words. Sindarin was said to be more changeful than the older tongue, however, and there were a number of regional 'dialects' of the tongue. The Sindarin spoken in Doriath was said to be the highest and most noble form of the language.

The tongue of the High Elves in Valinor, the first to be recorded in writing. It was never widely used in Middle-earth except among the Noldor; the related Eldarin language, Sindarin, was more commonly spoken.

By the Third Age, Quenya had become, in Middle-earth, a language used only on formal or state occasions by the Elves and the descendants of the Númenóreans

Anyhoo I hope that helps you!

A little, but I'm still confused. How can you tell the difference in the films?