In Zadig, Voltaire seems to portray women as mercurial in temperament and fickle in attitude. In this, both Semira and Azora are no exception. Why does Voltaire portray his female characters this way? It can be argued, of course, that Voltaire's misogyny presents itself quite clearly in his writing; however, Voltaire's philosophies on civil liberties greatly influenced the French and American revolutions. Clearly, one cannot conflate his delineation of societal excesses and abuses as proof of his biased view against women.
As with his protagonist, Zadig, Voltaire despised liars, cheats, and unscrupulous opportunists. However, he was too much of an idealist to accept the idea of original sin as an excuse for aberrant or immoral behavior. Like Montesquieu, he was suspicious of the common populace, claiming that democracy was not an enlightened option for the illiterate masses. Instead, Voltaire favored what he termed an enlightened absolutism, where a monarch would prevail over justice for all. Voltaire's passion for justice undergirds all Zadig's interactions with women in the story. In fact, Voltaire was thoroughly against the forced marriages of young girls in his time.
More about Voltaire here.
To return to the story, initially, Zadig is to marry the beauteous Semira. However, as a man of 'Integrity and Courage,' Zadig soon finds himself fighting off Orcan's goons. In the process, his left eye is wounded. Semira, who has thus far been 'incessant in her Prayers to the Gods' for her fiance's recovery, soon decides that she cannot marry a one-eyed man. On discovering that Semira has betrothed herself to Orcan instead, Zadig is broken-hearted and becomes a 'mere Skeleton,... sick almost to death for some Months afterwards.' When he recovers, he laments the capriciousness of noble ladies and decides to marry 'some substantial Citizen's daughter.'
However, his new wife, Azora, has a predilection for good-looking, young men. Zadig describes her as 'coquettish' (flirtatious). Azora, for her part, tries to proof her feminine constancy to Zadig by complaining about an instance of 'Female Falsehood.' Accordingly, Azora indignantly criticizes an old widow for failing to keep her vows to her dead husband. Zadig tests her with the help of his friend, Cador, and as expected, she fails the test. Zadig soon tires of her shrewish ways and divorces her.
Zadig found, by Experience, that the first thirty Days of Matrimony (as ’tis written in the Book of Zend) is Honey-Moon; but the second is all Wormwood. He was oblig’d, in short, as Azora grew such a Termagant, to sue out a Bill of Divorce, and to seek his Consolation for the future, in the Study of Nature.
The disposition to be unpredictable and also vengeful colors the portrayal of Arimaze's wife, a woman who frames Zadig. Jealous of his preference for the exceptionally gorgeous Queen Astarte, she inspires the king to suspect that Zadig and Astarte are already lovers.
Meanwhile, Zadig is wounded while saving a beautiful, Egyptian woman, Missouf, from the clutches of an abusive husband. Alas, all his efforts are rewarded by her with undue castigation. He terms her a 'Termagant and a Coquet' in return:
I have aveng’d your Cause, and deliver’d you out of the merciless Hands of the most outrageous Man I ever saw. Now, Madam, let me know your farther Will and Pleasure with me. You shall die, you Villain! You have murder’d my Love. Oh! I could tear your Heart out.
Again, Missouf's response to Zadig's courageous act demonstrates not Voltaire's misogyny, but his deep disapproval of the abuses women endure in his generation. Women are to subdue personal inclinations in any relationship, which leaves them open to both physical and emotional abuse. Since feminine reputations depend upon compliance to societal definitions of womanhood, many women are loath to rebel against the status quo. Thus, you see the supposed inconstancy and the baffling behavior exhibited by Missouf.
Further evidence of Voltaire's steady defense of women's rights can be seen in the instance Zadig convinces an Arabian woman not to throw herself upon her husband's funeral pyre.
Zadig remonstrated to Setoc, what a shocking Custom this was, and how directly repugnant to human Nature; by permitting young Widows, almost every Day, to become wilful Self-Murderers; when they might be of Service to their Country, either by the Addition of new Subjects, or by the Education of such as demanded their Maternal Indulgence.
Again, it is tradition, and not love which compels this widow, who asserts that her reputation will be ruined if she does not comply with expectations. Once more, Zadig jumps to the rescue. Our hero loves rescuing damsels in distress! This time, he becomes the benefactor of Arabian women when he succeeds in inspiring the creation of a Law which does away with widow sacrifice, a fitting nod to the author, himself a supporter of women's rights.
Twas to Zadig alone that the Arabian Dames were indebted for the Abolition, in one Hour, of a Custom so very inhuman, that had been practis’d for such a Number of Ages. Zadig, therefore, with the strictest Justice, was look’d upon by all the Fair Sex in Arabia, as their most bountiful Benefactor.
Please refer to the links below for more on Voltaire's portrayal of woman in his works.