Look at the following in LCE UI mod (I don't know how to explain what I want to explain):
resources/assets/lceui/tags/descriptions
resources/assets/minecraft/descriptions
TagResourceLoader.java
DescriptionResourceLoader.java

Basically, strings like block.minecraft.stained_glass.description won't work because there's no minecraft:stained_glass block, only minecraft:red_stained_glass, minecraft:orange_stained_glass etc. This goes for any block groups (wool, spawn eggs etc.)

I'm not going to implement this at all, as it's not efficient just to get a tip/description translation, I'm going to add tip overrides for these cases, specifying tags or list of items with the same description