That's right. A designated bilingual region does not mean that all employees are bilingual. It means that the ones who are bilingual have the right to choose the language they would like to use. That being said, there are unilingual positions in bilingual regions, so there are unilingual supervisors who supervise unilingual teams.
That is what amendment CPC-18 would change: a supervisor who supervises a unilingual team would be required to be bilingual.