It sounds like this student has a problem with expressive language; he is receiving and processing information correctly, he has trouble communicating what he knows. This could be a sign of a learning disability, or it could just be that he is sorting out the two languages in his environment. Lots of children who are raised bilingual have a slight delay in speaking, but they catch up to peers quickly, and are at an advantage because of their bilingualism!
Here is information on Children and Bilingualism from Reading Rockets.
Here is a collection of articles on Speech, Hearing and Language so you can read about normal speech development and warning signs of a bigger problem.
Finally, here is information about speech and language disorders.
If the problem persists and you suspect a processing problem, have this child evaluated by a speech language pathologist. Check the LD OnLine Yellow Pages for local listings.