why 你 说 中文 很 好 is incorrect?

e.g
你吃/喝得太快了 you eat /drink too fast .
你走得太慢了you walk too slow .
你回答得太晚了 you answer is too late
你写得太多了you write too much

吃得 ，喝得，走得， 回答得， 写得 so on

if you say 你说中文很好，then the meaning would be you say Chinese very good ,though we Chinese can understand the meaning ,but there has a little problem ,i suppose what you trying to say is "you speak Chinese very well“ right?
then you should say :"你的中文说得很好,you need to say 你的，你的means yours and you need to say 说得 instead of 说 说得means the level you say ,how well ?

“你说中文很好”这句话的中的形容词“很好”更像是在修饰“说”这个动词，可以理解为：你说中文这个行为很好。
改成“你的中文说得很好”会更恰当，此时“很好”才是修饰“你的中文（水平）”

你应该说：“你说中文说得很好 o或者 “你中文说得很好“
可以根据下面的这两个结构，然后自己实践：
1. S+V+得+A。
2.S+V+O+V+得+A

你要说：“你说中文说得很好 or 你中文说得很好“
Because in Chinese 得 is used to modify status and level, the formula:
1. S+V+得+A。
2.S+V+O+V+得+A

when you say: you speak Chinese well, the word ‘well’ is an adverb to discribe the verb 'speak'. In Chinese, when we discribe a verb, it should be connected by a word ‘得’ For example, 你“做得”很好，你说中文“说得“很好。 Then in oral Chinese a sentence like 你说中文说得很好，can be simplified as 你中文说得很好。

when you say: you speak Chinese well, the word ‘well’ is an adverb to discribe the verb 'speak'. In Chinese, when we discribe a verb, it should be connected by a word ‘得’ For example, 你“做得”很好，你说中文“说得“很好。 Then in oral Chinese a sentence like 你说中文说得很好，can be simplified as 你中文说得很好。

It's like the way you can't use an adjective to go with a verb, but adverb in English. We have S + Tobe + Adj, S + V + Adv, so in Chinese we have a formula to correct this error is: S + V + O + V + 得 + adj (你说中文说得很好。= You speak Mandarin very well.), not very good) or S + O + V + 得 + adj （你中文说得很好。） (so in this case, 得 + Adj = Adv (in English)

Thought about it a bit, "你说中文很好" can also be interpreted as "你说中文[这]很好", i.e. it's very good that you speak mandarin XD

Of course within contexts, no one would misunderstand you.

And thanks fatema for explaining! I didn't realize that Mandarin has also so many sov structures!

你说中文说得很好，根据结构。S+V+O+V+得+adj 或者S+O+V+得+ adj.