Interested in Language
We can say, "I've improved in science."
Can we say, "I've improved in English" ?
If the second sentence is incorrect, could you please explain why it is so, since the first and second sentences are the same except that the subject is different.
Both science and English are subjects taught at school. In this context, indeed you can say 'I've improved in English' - meaning your performance at school has got better in that subject.
But if you mean 'My English has improved' (with no necessary reference to performance at school, although your performance there will have improved) that's what you say.