Hello !
Sorry, maybe this is not really an "issue".. I'm just new at making datapacks
I can't find how to name a new tier in my datapack.
I created a tier, but I don't know where we define the "label"...
Can you help me please ?

Are you referring to translations for the attribute prefix?

For example, if you added an attribute with an id of mymod:awesome_attribute, the name of the tool might display as mymod:awesome_attribute.label Diamond Sword. The first part is a translation key, so you need to add a translation value in a lang file (assets/mymod/lang/en_us.json, for example) inside a resource pack:

{
   "tiered:reinforced.label": "Reinforced"
}

Let me know if you need any additional help.

I'm having the same issue, I've done every naming thing I can think of and every way to modify the en_us.json language file for the ids but I still just get mymod:new_attribute.label in the name field. Am I missing something? I followed the formate you laid out and just, nothing.