My question is about monographs:
the difficulties face students in learning english as a foreign language in university.
discuss the difficulties students face learning English?
what are the main problems can face students in learning english at university?
I believe your question is "what are the difficulties students face in learning english as a foreign language at a university?"
Study of a (foreign) language to attain high proficiency becomes progressively more difficult as we age. Indeed a child can attain native proficiency in any given language provided the right atmosphere and training. In comparison, at university level, study of a foreign language becomes rather difficult and only working knowledge may be attained.
The study of language is better accomplished by verbalizing it, or conversing with someone who is a native speaker.
Another faster route to learning, apart from conversing, is to use the language in other aspects of life, say other coursework. However the other coursework may not be available in that language.
Study of a language takes time and ideally it should be studied for a number of years.