Is there an English translation of Vigeneré's "Traicté des Chiffres"?
There is neither a „modern” French edition, nor an English translation, contemporary or modern. Time to learn some contemporary French. What's the use of attempting cryptoanalysis if you can't manage the historic version of a quite common language, in this case early modern French? Your approach works like the Traicté on its own linguistic grounds, not on yours.