Undercommon is a language that sees widespread use in the Darklands. Like Common, Undercommon is a blend of highly diverse languages that have combined over millennia to form a new, distinct tongue. The base structure and grammar of Undercommon is most similar to Dwarven, though in all other senses it has diverged so much to be mutually unintelligible. Much of the vocabulary has been adopted from such strange and disparate sources as Terran, Aklo, Elven, Draconic, Caligni, and Necril. As with Common, new vocabulary is freely added to the language when required.
Undercommon sees little use in the surface world. Even in the Darklands, most communities prefer to speak their own language and only use Undercommon when absolutely necessary. There is no standard dialect of Undercommon, and sometimes even those fluent in the language find it difficult to understand dialects specific to certain regions of the Darklands.