Should a window in the shower be different from the others?
The window pre 1980 is a regular window. Any post 1980 will be tempered (safety glass). Some come frosted glass, some don’t. If you want to do away with the window, spray paint the glass with black paint and close in the window with framing, insulation and moisture resistant drywall or hardibacker. Make it flush with the existing wall and tile over it. There isn’t any kind of waterproof window. If you keep it, make sure the tile slightly slopes away from the window into the shower. Use 100% silicone caulk to caulk the window frame to the tile and caulk the inside corners of the tile.
