Are you allowed to use the phrase "Courses of English"? I know it is commonly used as "courses in english" but I have seen it used in many places as "courses of"

For example, at Ohio State's website

"English 367 is the second of two composition courses that the University requires most undergraduates to take (the first is English 110). Because English 367 is a higher level course (generally taken by students in their second year), it offers texts and ideas that are more challenging and thought-provoking than you would find in a first-year writing course. And because it is writing course, students can expect to build on the skills they learned in the first-year writing course to improve composition, analysis, logical construction of arguments, coherence, and cohesion. The OSU English Department provides roughly thirty courses of English 367 per quarter."

So is "courses of" correct?
Generally, "courses of English" would be of and about the English language. "Courses in English" would be any course using English as the language of instruction.
There are 2 different ideas here:
First, there are courses in a subject area (such as English, History, Engineering, etc). A course is a general set of lessons at a particular level of difficulty in a subject.

Second, there is a single particular course, for example English 367. This one course can be offered many times. Each time is also called a course, not to be confused with a class, a single hour-long session within a course.

The text is using the second definition - there are many courses ( instances) of English 367 offered per quarter.
Students: Are you brave enough to let our tutors analyse your pronunciation?
Well what if the exact sentence was
"After taking many courses of english, he improved his writing skills"

Is that correct? (using it that way)
Students: We have free audio pronunciation exercises.
I would use "in" because you mean the subject area - English.