I gave some item with LocName.(named in us: Prismarine Pickaxe, jp: プリズマリンのツルハシ)I only see this messeage.

 [@: Given [citem.pickaxePrismarine.name] * 1 to <UserName>]

(in Vanilla Minecraft, I could see the Customized name, such as "Prismarine Pickaxe".)

But in my item was still named original name

Used Command: /give @p minecraft:diamond_pickaxe 1 1 {display:{LocName:"citem.pickaxePrismarine.name"},Unbreakable: 1,HideFlags: 4}