The three-letter code points to the Ethnologue, 14th edition. The link will allow you to find more recent editions.
Press List to generate the list of sources. Symbols and widely cited sources are explained below.
Nilo-Saharan, Kordofanian, Khoi-san
Turkic, Mongolian, Tungusic, Japanese, Korean
Pidgins and creoles
(biggest contributors first; abbreviations in boldface):