The Kai-Souk languages are a language family on mainland Southeast Asia, also known as Indochina. These languages are the only extant branch of the Song languages, except for a few (>100) native speakers of other branches. Souk is the most widely-spoken of the family; the remaining Kai-Souk languages are spoken almost exclusively by hill peoples and isolated islanders.
The language family is named such due to the fact that most of the languages' ethnic groups are closely related to the Kai people; in fact, about 20% of Kai people do not speak Souk as a native language, especially islanders. The Kai-Souk languages were all once simple dialects of Old Souk, which eventually evolved into proper languages mutually unintelligible with Souk, which is itself the direct descendant of Old Souk; thus Souk is described as the oldest language of its family.
The Kai-Souk languages are generally transcribed according to the Kai-Souk Colonial Alphabet.