After 1 day Searching i got 2 way You Can Apply Decal On Translucent Materials
- you can make a blueprint actor and give your Decal Material On that and spawn it where ever you want …
– Note 1: the actor which you spawning decal on it if moving . simply “attach actor to actor” OR “attach actor to component”
–Note 2. THIS UGLY solvation just work on somethings Are Like Plan … so the BP_Decal you made will Fix on that … BUT if you have something like Circle , it will not work as you want
Way 2 (Recommended by ME 
). All OF Us Know the Decals Will not Render On Translucent So what we can Do ?
→ Make a material then give the channel Surface And Masked.
then on Graph just give Some opacity To Opacity Input
Note 1. Engine Just Modify the Masked For Decals Which They Have Opacity Above " 0.4 " … (Care About That)
Note 2. You Can To Your Glass Some Color If You Want
EDIT :
Note 3 : 
You Have To Go Edit > Project Setting > Rendering > Anti-Aliasing Method To MSAA ( For Working Opacity Mask Between 0 and 1 )
The Mask make Problem With Niagara => if Glass is between your camera and Niagara … the mask material will Not Render That ( HAHA)
Result OF Way 2.
