Complex sentence: It is now generally recognised that the letters are not a verbatim translation from the Portuguese, but instead a work of fiction by the comte de Guilleragues, a confidante of Madame de Sablé who served as ambassador to Constantinople from 1677 to his death in 1685.
Split into simpler sentences: It is now generally recognized that the letters are not a verbatim translation from the Portuguese, but instead a work of fiction by the comte de Guilleragues. The Comte de Guilleragues was a confident of Madame de Sablé and served as ambassador to Constantinople from 1677 to his death in 1685.