Is it appropriate to say “I speak good English” or “I speak correct English”?
I believe there can be varied replies depending on context, so let me narrow it a little; let’s say I want to convey how well I speak English.
I suggest you think about the opposites of good and correct.
The opposite of good is bad. If you feel you speak reasonably good English, then, by all means, say so.
On the other hand, the opposite of correct is incorrect or wrong, and, in this context correct also carries the implication of perfect or without fault. I would be very surprised if anyone could claim to speak perfect English, without fault. Few native speakers would even claim to speak completely correct English.
One might talk of a particular English expression, phrase, sentence, etc. being correct, or of something being correct usage in a particular context - but not of one's English being completely correct overall.
I would suggest that you speak English well. "I speak good English," is a proper usage, but it sounds more refined to say "I speak English very well."
I really prefer the adverb to describe the verb speak, rather than an adjective to describe the noun English.
Or, for that matter, you might even say fluently. That tends to be the proper terminology when speaking of a foreign language.
For instance, I happend to speak three languages: I speak English natively. I speak Spanish fluently. And, I speak Italian well.
Notice that in all three, I've used the adverb to modify the way I speak. I did not make a judgement on the language itself.
I do use a different construct where I use an adjective, though. I will say something like: My Spanish is excellent. My Italian is good. I am not judging the language, but rather the way I personally speak it.
You could say that "good English" might be used as an answer to a question ("How good is your English ? / Pretty good !"). "Correct English" can be used as a way of describing how good the grammar in a text it is ("It seems that their English is pretty correct..."). So these are the main ways in which i think the difference between how these two expressions can be used. Hope this helped you !
If you look up "language" in a collocations dictionary, you will see only "good" listed there: http://www.ozdic.com/collocation-dictionary/english
Therefore, the answer to your question is "to speak good English".
If you need less informal words, "excellent, fluent, perfect" will do.
If you speak proper English does that mean that people who aren't as good as you are at speaking English speak improper English?
English is a noun which describes a certain language. How can a language be good? Answer - it can't. You either speak English well or you don't speak it well.
Saying "proper English" doesn't help because what is proper in some contexts might not be proper in others. And not saying something properly does not make it improper.