Wikipedia
Wenzhounese , also known as Oujiang or Dong'ou (東甌), is the speech of Wenzhou, the southern prefecture of Zhejiang, China. Nicknamed the "Devil's Language" for its complexity and difficulty, it is the most divergent division of Wu Chinese, with little to no mutual intelligibility with other Wu dialects or any other variety of Chinese. It features noticeable elements of Min dialects, which is spoken to the south in Fujian. Oujiang is sometimes used as the broad umbrella term, reserving Wenzhou for Wenzhounese proper in sensu stricto.
Due to its long history and the isolation of the region in which it is spoken, Wenzhounese is so unusual in its phonology that it has the reputation of being the least comprehensible dialect for an average Mandarin speaker. It preserves a large amount of vocabulary of classical Chinese lost elsewhere, earning itself the nickname "the living fossil", and has distinct grammatical differences from Mandarin.
Wenzhounese speakers who have studied Japanese and Korean note that there are words that sound like Japanese or Korean but have different meanings.
Wenzhounese is one of five varieties of Chinese other than Standard Mandarin used for broadcasting by China Radio International, alongside Cantonese, Hokkien, Teochew, and Hakka.