"He speaks good English"—ungrammatical?

"He speaks good English" is perfectly grammatical as long as you keep in mind that good is an adjective modifying English. Thought experiment: replace good with proper. You probably have no problem with the following sentence:

He speaks proper English.

Why is that okay while "He speaks good English" isn't? If you fail to see your inconsistency, you're a proper idiot. Basically, the grammar in question is:

He speaks [adjective] English.

This means you can say things like:

He speaks horrible English.
He speaks fantastic English.
He speaks perfect English.
He speaks accented English.

I think back on an incident during my freshman year in college. Two friends of mine, Mike and Paul, had a moment when I used that exact sentence: "He speaks good English." They looked at each other and smirked, effectively closing me off from the group so they could share their misguidedly conspiratorial mirth: Kevin was being ironically ungrammatical! In truth, I'd said nothing wrong, and even back then, I fucking hated being "corrected" or called out when I wasn't wrong. So fuck you both, Mike and Paul. You were both wrong to sneer.

Grammar hurts sometimes.

But here's a philosophical question: are you conveying the same meaning if you say "He speaks good English" or "He speaks English well"? A hairsplitter might argue that, in the first sentence, you're referring somewhat prescriptively to a high quality of English—a respectable dialect or something—while the second sentence is referring specifically to a speaker's proficiency, not to the quality of the language spoken. A person could conceivably be a proficient speaker of a rough-and-tumble dialect of English that refined folks would not consider "good" English.

That said, I think the more natural answer, pace the hairsplitters, would be that "He speaks good English" and "He speaks English well" convey the same information. In either case, if you lack English proficiency, you can be said neither to "speak good English" nor to "speak English well." There's no need to overthink the issue.

I have spoken.