Is an English translation available?
Unfortunately, Vigenère's "Traicté Des Chiffres, ou Secretes Manieres D'escrire" is not yet available in English.
Covering many disparate subjects, it is a rambling 600-page work that introduces some important advances in cryptography. For example, having the ciphertext itself serve as a key after a priming key. The autokey ciphers outlined in Vigenère's book, according to David Kahn, "were entirely forgotten and only entered the stream of cryptology late in the 19th century after they were reinvented."[1]
Vigenère was a prolific writer. The lengthiness and many digressions of "Traicté Des Chiffres, ou Secretes Manieres D'escrire" have contributed to its obscurity. It seems that no one has wanted to translate this very long and strange work that attempts to interrelate alchemy, Japanese ideograms, God, magic, and genuine advances in cryptology. Nevertheless, many have found this book utterly fascinating.
[1] Kahn, D. (1967). The Codebreakers: The Story of Secret Writing (1st ed.). The Macmillan Company. pp. 147, 148.