While the base Item Descriptions mod only intends to support blocks, items, tags, and entities that exist in vanilla Minecraft and the Fabric/NeoForge Common tags, additional mod support is encouraged!
Mod Developers
If you want your mod to support Item Descriptions, I would encourage including Item Descriptions translations in your mod itself.
Modpack Developers
If you have mods that you want to support Item Descriptions, you can either make your own custom resource pack with Item Descriptions translations, or contribute them to Mod Descriptions as a Pull Request, which is focused on providing descriptions for as many mods as possible.
Data/Resource Pack Developers
If you want your custom items to have custom Item Descriptions, you can make your own custom resource pack and follow the guides for Custom Model Data and/or Player Heads.
Translators
If you're interested in translating Item Descriptions to your language, please send in a Pull Request with these descriptions to the main mod.