I wasn't trying to say that it was cheating on the part of candidates, but that people often tend to overestimate their knowledge of the other language. If anyone had to evaluate my English, some people would say that I'm not completely bilingual.
As for the other aspect you talked about, that there are still situations in which we aren't directly understood in our language, the Supreme Court is the exception in the Official Languages Act. Section 16 states that, at the Supreme Court, they don't need to understand directly and that they can do it through interpretation. However, the act provides that all other federal courts have an obligation to understand directly.