Men’s shirts have the buttons on the right, but women’s shirts have the buttons on the left.
During Victorian era, women particularly wealthy women, wore elaborate items and often enjoyed the luxury of being dressed by a servant. In that case, it was easier for the assistant to have the buttons on the right side (when facing the woman being dressed) with the assumption that the servant was right-handed, as most people were believed to be. Men usually dressed themselves, hence the buttons on the other side.
Other possible explanation is,
A right-handed man could pull his weapon out with his primary hand and unbutton with the secondary. Women usually hold a child on their left side to free up a dominant hand and a shirt that opens on the right makes breastfeeding easier.
