I'm not sure if InvisibleShield has a template for Tamagotchi iD Ls, but you can actually use a normal screen protector and cut out to its screen size.
As for the USB infrared, you can actually get anything as they all work the same. Getting it to work can be kind of tricky, but if you get the timing right you'll be customizing your iD L in no time.
Just like any smooth, lint-free cloth you use to clean your computer or phone screens will do. If you buy a screen protector, I think they come with a small piece of wiping cloth for you to clean the screen first before putting the protector in.
If you need translations, just shoot me a PM.

Enjoy your iD L! What colour did you get?