As with other occasions in the series, the nature of translator microbes creates plot problems. The microbes don't allow a person to speak a new language, they merely let a person be understood by people who don't know the speaker's language. Therefore, when Crichton masquerades as a Peacekeeper, he is speaking English. It should be obvious to everyone he comes across that he is not speaking Peacekeeperese, because to their eyes his mouth is moving out of sync like a badly dubbed foreign movie. His masquerade should have been uncovered much earlier than it actually was.