Returns true if the given lookup is a valid linguist lookup.

def is_linguist_lookup(self, lookup):
        """
        Returns true if the given lookup is a valid linguist lookup.
        """
        field = utils.get_field_name_from_lookup(lookup)

        # To keep default behavior with "FieldError: Cannot resolve keyword".
        if (
            field not in self.concrete_field_names
            and field in self.linguist_field_names
        ):
            return True

        return False