Complex sentence: Toland claimed to have a personal copy of the manuscript and passed his version to the circle of Jean Rousset in France, who published a French translation, which was taken slightly seriously by some, but not by Voltaire who issued a satirical reply.
Split into simpler sentences: Toland claimed to have a personal copy of the manuscript which he passed to the circle of Jean Rousset in France. Rumours that it was then translated into French were taken seriously by some: however, not by Voltaire who issued a satirical reply.