My wife has only given birth to daughters. Is it right for me to take another wife to have a son?

A child's sex is Allah's decree, not the wife's fault, so making it a reason for polygyny wrongs her feelings. Daughters are a mercy and a trust, and raising them well is a great honour. Blaming your wife for something that was not her choice leaves a deep wound. If you still consider polygyny, it must rest on the right intention and ability, not family pressure or simply wanting a son. Talk with your wife with full respect, and cherish the children Allah has given you. Pray often for righteous offspring, because a child's goodness is not determined by sex. See critical wisdom.