Kung window lang ang concern mo, you have to ask yourself, do you still want ambient light going in? or do you want to seal the window completely?
If you want to have ambient light, definitely double plate glass is called for but remember, it is only as efficient as the frame and sills you will install, as well as the wall the window will go into. If the wall isn't exactly soundproofed to begin with, useless ang double plate glass construction.
You can also consider closing off the window by using the methods and materials described in the thread such as gypsum boards and rockwool/fiberglass. If the wall in question is concrete, them consider cementing the hole completely since soundproofing is dependent on the mass of the materials you will be using.