In some places, you are required to have windows or an approved ventilation system in your bathroom, though codes and laws vary by state, county, and location.
Where bathroom windows are required or exist, the glass does have to be tempered safety glass. This is especially true for skylight windows and any windows or glass within five feet of the shower or bathtub.
Whether it’s mandatory in your locality or not, we do strongly advise having a ventilation system.