Well, being proficient in English at a higher level, such as Standard American English, gives a great advantage for academic success because it enables understanding and usage of complex ideas and concepts.
Good English skills also provide an important foundation of knowledge for understanding and writing research projects and academic essays, and reading books and articles.
Speaking, listening, writing, and reading are essential skills in academia, and a solid grasp of the English language can help people communicate their ideas more clearly, articulate their thoughts more clearly through writing, and understand material better when studying.