Chinese can be divided into thirteen kinds, among which Mandarin is the most widely used. The rest are Cantonese, Hakka, Minnan and so on. Some southern dialects are very different from Mandarin, such as Minnan dialect. For many Chinese people, Minnan dialect is tantamount to a foreign language.

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In both of the last two sentences, you need to insert the definite article "the" before "Minnan": "the Minnan dialect." Also, the word "kinds" in the first sentence is much more informal in tone than the rest of the passage. I would suggest that you sub in "dialects."