My take on this is that the speaker is implying that [s]he is saying something in a language other than the usual English and makes a faux apology the same as one might do who dropped a Latin or Greek phrase into a casual conversation. Why French? I think it's an arbitrary choice because it's the most likely to be a second language for English speakers. I have never had the impression that there was any derogatory implication towards France, the French, their mores or their language. I could be wrong.