Macro-Siouan languages
In the 19th century, Robert Latham suggested that the Siouan languages are related to the Caddoan and Iroquoian languages. In 1931, Louis Allen presented the first list of systematic correspondences between a set of 25 lexical items in Siouan and Iroquoian. In the 1960s and 1970s, Wallace Chafe further explored the link between Siouan and Caddoan languages. In the 1990s, Marianne Mithun compared the morphology and syntax of all the three families. At present, the Macro-Siouan hypothesis based on relations among Siouan, Caddoan, and Iroquoian is not universally accepted as proven.
Bidayuh
The Serian Bidayuhs have a distinct dialect known as the "Bukar & Sadong language" Bidayuh, which is not intelligible to Bidayuhs from other Districts. Here are some examples of the differences in the various dialects spoken in Serian, with their English and Malay equivalents. Also included are two Philippine languages, Kapampangan and Tagalog: