why not just leave it? I think french doors are nice. Put up a curtain with high placed rod inside the room and you have your privacy!
just place the rods so they are beyond the width of the door. Put some grommet panelling on it and baam! you have yourself a nice bedroom. Make sure the panels are 3x the width of the door. it'll look nicer that way. Maybe add plantation shutters to the doors. Then you can have sheer panels
Maybe you don't like curtains huh? I guess they sell glass paint that can be taken off. You can paint them and put different paint over for designs or something. I think they come off, but not sure how much work it will be.