[T]he Officer was speaking French, and certainly neither the soldier nor the prisoner understood a word of French.

The Officer’s use of French when first describing the apparatus to the Traveler emphasizes his belief that he and the other man are insiders while the condemned man and even the soldier are outsiders. It’s horrifically ironic that the Officer describes the process and instrument of execution in a language the condemned man can’t understand. Since the condemned man is described as stupid-looking, it’s implied that the Officer doesn’t regard him as an equal in either rank or humanity. To use a language foreign to the man reinforces his status as an outsider, someone with no access to or even understanding of the Officer or his intentions. The fact that the Traveler speaks French demonstrates how the Officer includes him within his own insider status. This is significant since the Officer understands why the Traveler is there and seeks to sway him to his own beliefs and values rather than the current Commandant’s in order to maintain his own insider status. 

The Traveler would have liked to say something appreciative, but all he could see was a labyrinth of lines crossing and recrossing each other. “I can’t make it out.”

When the Officer reveals the plans for the apparatus to the Traveler near the beginning of the story, the words and diagrams are found to be indecipherable to everyone but the Officer and serve as a symbol of the Traveler’s unwillingness to step into the Officer’s inner circle. Because the former Commandant is dead, the Officer is the only one left who can translate the plans, maintain the apparatus, and carry out the executions. Although he enjoys the power that comes from being an insider, the Officer understands that his power is under threat by the new Commandant and acts accordingly. He tries to enlist the Traveler to his way of thinking and treats him as a fellow insider by confiding his disdain for the new Commandant, speaking French as a language meant to exclude everyone except the Traveler, and showing him the former Commandant’s plans. The fact that the plans appear as gibberish to the Traveler foreshadows how he will never be drawn into the Officer’s inner circle and that the Officer is doomed to lose his status as an insider.