Nitpick: Gilina insists that Crichton not face the cell's camera while she talks to him, since she is overriding the sound, but not the picture, and presumably she's worried that someone might be able to lip read what he's saying. But John is speaking in English, not Sebacean. Do translator microbes bestow the ability to lip read unknown languages as well as the spoken word? He certainly couldn't lip read Aeryn in the earlier episode "Through The Looking Glass", nor she him.
As a side note to this, surely any of the Peacekeeper guards or officers would notice that what they see Crichton say and what they hear is out of sync, and tag him as an imposter from the start? The same would apply to the earlier episode "A Bug's Life" when Crichton again poses as a Peacekeeper captain.