"I like to study the English too because it is fun!"
Correct if "the English" means "the people, culture, or history of England", or "the interesting or peculiar way some speaker, author, or group uses the English language", or "the athletic sporting technique of body English".
Mostly incorrect, excepting for if "the English" is short for "the English textbook I'm assigned", (supposing group of students is discussing the merits of a stack of their various classroom textbooks), as here "English" would be an adjective, (describing the noun book), that's momentarily promoted to a noun. Outside of such a bookish context, this usage would be as incorrect as starting with "I like the French Fries with ketchup", and abbreviating it to "I like the French with ketchup".
Incorrect if "the English" means which kind of classroom schooling one prefers -- here English is used in the most abstract sense possible, and such usage therefore lacks the sort of distinctive attributes that require using an article; in other words, it's a one-of-a-kind object, there is only one "English" in the universe.
Articles distinguish between available quantities of generally non-unique objects. The article "A" means one among many, the article "The" means the only one of a specific or particular object that's at hand or currently exists, and no article is reserved for unique abstractions.