I totally lost. 他不快说汉语 -> what's wrong in this sentence?

I know 他汉语说得不快 is right one. But what makes this sentence (他不快说汉语 ) incorrect?

submitted by /u/imnagini
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from r/ChineseLanguage: a community for people who are studying, teaching, or interested in Chinese! https://www.reddit.com/r/ChineseLanguage/comments/a79hob/i_totally_lost_他不快说汉语_whats_wrong_in_this_sentence/

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