Languages of the Eldar

Qenya: The ancestral tongue of the Eldar, developed by those who dwelt in Valinor (the Undying Lands). Qenya is rarely used to converse in, in the third age, it is rather used in official names and to preserve lore and western expressions.

Sindarin: The language of the Teleri, those of the Eldar who never reached Valinor. When the Noldori elves returned to Middle Earth, they adopted this language (even though they found Qenya more beautiful). It was subject to several dialects, though the roots remained the same. Before the downfall of Númenor, many of those men spoke Sindarin. However, the exiles of Númenor kept the tradition of learning and knowing the language.

Silvan: One of the more prominent dialects of Sindarin. It's primarily used by the elves of Mirkwood and Lothlorien, though the Lords and Ladies of those regions do not necessarily use it as their primary tongue.

Westron: The 'common' speech of Middle Earth. It has heavy influences from Sindarin and the tongue of Númenor and many dialects of its own.

Dalish: A dialect of Westron used by the men of Dale in the north, living close to Erebor and the Lonely Mountain.
Rohirric: A dialect of Westron using Sindarin elements used by the Rohirrim, the Horse Lords of Rohan.
Dunlending: Another language that has basis in Westron, despite being very different from it and the language of the Númenorians.