If they haven't encountered those expressions, those ways of using language orally, then they are going to have a great deal of difficulty in processing them in writing. So at many different levels, control over the oral language is a prerequisite to making continued progress with literacy. But at the same time, the best way to acquire some of these oral language skills is actually by reading. Reading is the major input to oral language after kids are eight or nine. So in that sense I think the connections are multiple and organic.
Bilingual education has different meanings in different contexts.
For example in Latin America the vast majority of bilingual schools are elite schools. This is also true in countries like Turkey and Russia. In the U.S. however, bilingual education is largely compensatory folk education, not elite. Most of those countries do intensive target language instruction, as for example, in Israel where both adults and children have access to intensive courses in order to learn Hebrew. In Europe the traditional approach to immigrants has only rarely been bilingual education.