While there is no "official" language for the United States (and thus California), it is widely considered that English is the de facto national language. It is the majority language for both the country and California.
So having difficulty with English is a really, really bad thing for these students.
Having difficultu with English is definitely really bad. Especially in California, where poor English skills can continue to thrive in immigrant populations after schooling and lead to less opportunities in general.
So having difficulty with English is a really, really bad thing for these students.