Elvish languages
Tolkien conceived a family tree of Elvish languages, all descending from a common ancestor called Primitive Quendian. He worked extensively on how the languages diverged from Primitive Quendian over time, in phonology and grammar, in imitation of the development of real language families. In addition to Quenya and Sindarin, he sketched several other Elvish languages in far less detail, such as Telerin, Nandorin, and Avarin.