When the Chief asks 99 how well she speaks German, she replies that she is fluent. However, in "Rub-A-Dub-Dub... Three Spies in a Sub", she wasn't able to understand any of Siegfried's statements in German, and repeatedly asked Max to translate.
When Maxwell Smart is first asked by the Chief to prove he can speak German he spouts complete gibberish. Later when he speaks German he speaks a few words only and with a horrible accent.