I have found this particular form of decorate windows . First of all it is worth clarifying that not in any type of bathroom or environment can be seen well, you must take into account where that window on the outside, the size, the light that enters and the type of environment.
Assembling a mirror in front of a window can be a good idea for a bathroom, especially if a lot of light comes in, it will give you another impression to look in the mirror with natural light entering through the window. You can also do it in your room but in this case I advise it to be more delicate.
These photos will serve to give you ideas of where and how to mount mirrors in front of windows.