[VanShuyten]

Actually, "good" is an adjective which modifies the noun "English", so this usage is correct. "Well" is an adverb which works on the verb "speak."

Thank you, thank you! I'll be here all weekend.

[Clint N. Suhks]

If you are saying that english is “good,” I agree-both with your sentiment and with your assertion that good is the proper adjective for the word english. However, if you’re talking about how english is spoken, written, heard, etc., those would require adverbs to describe, such as “well” as opposed to “good.” For example, how are you? I am well.

(How where when why) are adverbs that answer the question.

Now be good!

And be well...

[Melas]

Whether English is good or not is not at question in that sentence. What the author was looking for was an adverb that modified the action of speaking. English didn’t require modification, the speaking of it did. You could in theory speak good English, poorly.