Was there really a journal of Paris? Was it some kind of English language paper for ex-pats, which would explain why Franklin was writing an letter in English to it? Or was he writing a letter in English to a "Journal de Paris", assuming that anybody educated enough to read was educated enough to read English? Or is the whole "journal" thing just a joke, and it's just a pamphlet for general publication making fun of the Parisians (which would also explain the English language)?
On a broader note, Franklin and Jefferson spent an awful lot of time in Paris, but I never run across any letters or writings of theirs in French. Do these things exist but just don't show up often, was there some kind of social faux pas that explains this, or was their French just kind of sucky?