Will the developer of an English-Arabic dictionary app that uses a female voice for pronouncing words be sinful, given that the app has been downloaded over one million times, and will he bear the sin of the users if that is unlawful?

A woman's voice is not in itself 'awrah (something that must be covered or concealed), but it is forbidden to display it to non-mahram men if it is done in a way that incites fitnah (temptation or discord). Marketing and promotion using a woman's voice and appearance is a product of the West and contrary to Islamic law, which came to protect souls from inciting desires. Therefore, the feature of a woman's voice should be avoided in applications and replaced with a man's voice, or effects should be added to a woman's voice to strip it of any allure. A believer strives to rectify people's affairs and repel fitnah.