Tag Fixes currently adds tags to items, blocks and fluids that are missing, incomplete or broken in their respective mod to improve compatibility between mods. Primarily modpack utility, especially ore/material unification.
Tag Fixes also adds localization to over 2773 tags from 63 different mods missing them, which can appear in recipes. For instance, a tag appearing unlocalized in recipes as "#farmersdelight:tools/knives" instead of localized as "Knives", as it is with this mod.
Localizations are located in common/src/main/resources/assets/tagfixes/lang/en_us.json. This is the main file to edit to add localizations to tags missing them. Make a pull request to contribute localizations to either this file or other language files.
Tags are located in common/src/main/resources/data. They follow standard data-driven, each folder for a mod, containing folders and tag files inside. For instance, to add axes to the #forge:tools/axes tag, you will need to modify the file that is in forge/tags/items/tools/axes.json. Make a pull request to contribute tags.
https://www.curseforge.com/minecraft/mc-mods/tag-fixes