Looking on the internet deeply has found these results:

He is really good in English is the most popular phrase on the web.

He is really good at English 137,200 results on the web	He is really good in English 1203,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Your husband is really good at keeping secrets, especially from you. Charlotte is really good at English and she can help both of us on this presentation. Yes. I'm really good at English. Derek is really good at this kind of thing. Some smart people can't translate their smarts to other people, but he is really good at explaining things, and he makes you want to learn more. Scientology is really good at making you think that you are a scoundrel. Because she is really good at coming up with new stuff. She is really good at planning trips.	Derek is really good at this kind of thing. And he is really, really good for me. She is really good in singing. Yes. I'm really good at English. Some smart people can't translate their smarts to other people, but he is really good at explaining things, and he makes you want to learn more. I just think he is really good for you. One of the reasons why it's easy to appreciate British humour is, if you speak really properly good English, which you... Charlotte is really good at English and she can help both of us on this presentation.

He is really good at English

137,200 results on the web

He is really good in English

1203,000 results on the web

More popular!

Your husband is really good at keeping secrets, especially from you.
Charlotte is really good at English and she can help both of us on this presentation.
Yes. I'm really good at English.
Derek is really good at this kind of thing.
Some smart people can't translate their smarts to other people, but he is really good at explaining things, and he makes you want to learn more.
Scientology is really good at making you think that you are a scoundrel.
Because she is really good at coming up with new stuff.
She is really good at planning trips.

Derek is really good at this kind of thing.
And he is really, really good for me.
She is really good in singing.
Yes. I'm really good at English.
Some smart people can't translate their smarts to other people, but he is really good at explaining things, and he makes you want to learn more.
I just think he is really good for you.
One of the reasons why it's easy to appreciate British humour is, if you speak really properly good English, which you...
Charlotte is really good at English and she can help both of us on this presentation.