i have a lang.json under my assets and my mod_id is nightfuel
public static final String MOD_ID = "nightfuel";
here is my lang.json
{
"item.nightfuel.nightmare_fuel": "Nightmare Fuel",
"item.nightfuel.living_wood_shard": "Living Wood Shard",
"item.nightfuel.dark_tatters": "Dark Tatters",
"item.nightfuel.red_gem": "Red Gem",
"item.nightfuel.purple_gem": "Purple Gem",
"item.nightfuel.orange_gem": "Orange Gem",
"item.nightfuel.yellow_gem": "Yellow Gem",
"item.nightfuel.blue_gem": "Blue Gem",
"item.nightfuel.bullet": "Bullet",
"item.nightfuel.cartridge": "Cartridge",
"item.nightfuel.firing_mechanism": "Firing Mechanism",
"item.nightfuel.revolver": "Revolver",
"item.nightfuel.dark_sword": "Dark Sword",
"item.nightfuel.fire_staff": "Fire Staff",
"item.nightfuel.ice_staff": "Ice Staff",
"item.nightfuel.light_staff": "Light Staff",
"item.nightfuel.dark_staff": "Dark Staff",
"item.nightfuel.blade_staff": "Blade Staff",
"item.nightfuel.shadow_chestplate": "Shadow PlateMail",
"item.nightfuel.shadow_leggings": "Shadow Chausses",
"item.nightfuel.shadow_boots": "Shadow solleret",
"item.nightfuel.ruby_crown": "Ruby Crown",
"item.nightfuel.flare_earrings": "Flare Earrings",
"item.nightfuel.shadow_crown": "Shadow Crown",
"item.nightfuel.dark_pickaxe_axe": "Dark Pickaxe-axe",
"item.nightfuel.umbric_paper": "Umbric Paper",
"item.nightfuel.dark_ink": "Dark Ink",
"item.nightfuel.fire_scroll": "Fire Scroll",
"item.nightfuel.dark_scroll": "Dark Scroll",
"item.nightfuel.hunger_scroll": "Hunger Scroll",
"item.nightfuel.haste_scroll": "Haste Scroll",
"item.nightfuel.rage_scroll": "Rage Scroll",
"item.nightfuel.shadow_heart": "Shadow Heart",
"block.nightfuel.living_wood": "Living Wood",
"block.nightfuel.living_leaves": "Living Leaves",
"block.nightfuel.purple_rock": "Purple Rock",
"block.nightfuel.purple_grass": "Purple Grass",
"itemGroup.Nightmare": "Nightmare"
}