Would you say that both of the following sentences are equally correct and natural?

He is very good at English.
He is very good in English.

My dictionaries show only at with good. Please shed some light on this.

Thanks a lot,

Yes, both are OK. This discussion appears here probably a dozen times. 'At' is better than 'in' only when speaking of a quite restricted ability (so that it doesn't have 'size' or 'dimension'): 'he's very good at long division.'
Mr. Tom: If you go to "Search the site" and type in "good at/in," you will find many interesting ideas about this subject. You should probably say, "I am good AT English." There is no "rule." Most native speakers have decided to use "at." If you use "in," you are not "wrong." But some native speakers would feel that you are not speaking idiomatic English. ("idiomatic" = natural sounding to a native speaker.) For example, it is idiomatic to say: I am proficient IN English. In other words, Mr. Tom, you will simply have to read widely and listen to native speakers.