Fangyan

During this time the language has diversified into a number of so-called fangyan which share the same written form but are radically different in phonology, to such an extent that the spoken fangyan are not mutually intelligible.

Source: wiktionary

If analyzed by the standards applied to languages in Europe or South Asia, these fangyan would be classified as branches of the Sinitic group. Speakers from any one of the major fangyan are incapable of conversing with speakers from those of any of the other major fangyan.

Source: wiktionary

One consequence of such misinformation is the tendency to view Mandarin as a single Chinese language, and fangyan as subdivisions of it.[…] Actually, Chao Yuen Ren (2002b, 82) himself, in a 1959 lecture at National Taiwan University, accepted that 'fangyan in the broad sense if the term refers to fundamentally different languages'.

Source: wiktionary