Strangely, two main linguistic groups of the San Chay, the San Chi and the Cao Lan, today speak different languages.  The language of the Cao Lan is classified as part of  the Tay-Thai linguistic group.  No doubt at one time all the San Chay spoke a common language (see History).  They still can understand each other to some extent.  The Cao Lan love songs, for example, are in San Chi, a Cantonese dialect.  In some areas, notably in the Bac Giang province, the San Chi use Cao Lan for ceremonial purposes.  In Quang Ninh province, until recently, elderly San Chi still spoke Cao Lan; however, this bilingual ability is today quite rare.

            The Tay-Thai languages are spoken by eight of Vietnam's 54 officially recognized ethnic groups.  The Thai peoples in Vietnam are related to the Thais of Thailand, but in most cases this realationship is distant.  These groups are the Tay, Thai, Nung, San Chay, Giay, Lao, Lu and Bo Y.  Some of these groups have been living in what is now Vietnam for thousands of years.  Cantonese is part of the Han group of languages of the Sino_Tibetan Language family

            This means that the San Chay languages are linguistically unrelated to Vietnamese, the national language of the country.