What is the difference (nuance) between these two sentences?
'To study English is not easy.'
'Studying English is not easy.'
Parth, that's not quite right. To study (the infinitive) and studying (the verbal noun) have the same function in the sentence so are semantically identical. In both sentences the subject is the noun clause, 'To study English' and 'Studying English', followed by the predicate, 'is not easy'. It's just the syntactical makeup of that noun clause that differs. So here the question is about connotation and about which is more natural in English.
The verbal noun is more natural here. Using the infinitive adds emphasis and suggests a different sort of meaning: like 'To study English is never an easy task', or 'To study English is a necessity these days'.