The expression "without an interpreter" appears in subsection 16(1) of the Official Languages Act. That section concerns federal courts other than the Supreme Court of Canada. I believe it provides a quite general indication, without being specific or regulatory, in describing adequate linguistic proficiency to do the job. It is not about the level of evaluation. All kinds of methods can be used to determine whether a person is able to do the work without an interpreter.
This is a phrase that has been taken from the Official Languages Act, and I believe it is entirely appropriate.