Sylvan

Sylvan is a language created by the Fey Lord Silvarion, originally for use by him and his fairy compatriots to patrol in and converse with the forests of the mortal plane. However, over time it eventually became the language of the Fey, and the language to be used for communicating with any beasts and/or plants. Though they cannot respond without the use of magic, even the simplest plants and animals seem to respond to words spoken in Sylvan. 
Sylvan has a sing-songy sound to it when spoken, as the words tend to blend together into a strong, rather than a series of individual words. This makes the language very good at getting across tone and general concepts, but more difficult to get specifics like directions or descriptions. For example, someone speaking Sylvan is more likely to call a werewolf and sometimes-wolf.