You make a good point, but we can use empirical data to settle it. Look at the greatest writers in a given language. Ask if they were monolingual or not.
For one instance, I (personally) am not aware of Shakespeare knowing any languages other than English; however, it may be that all educated people in that era knew Latin, and so the many great English writer so the past support your hypothesis.
For one instance, I (personally) am not aware of Shakespeare knowing any languages other than English; however, it may be that all educated people in that era knew Latin, and so the many great English writer so the past support your hypothesis.