As of Taterzens version 1.8.2 on Minecraft 1.18.1, entity.taterzens.npc does not have an English translation as it does not appear in the en_us.json file itself.

This occurs regardless of the mod loader or whether the mod is running in single player or on a server.

Would this translation be used in vanilla?

Should be a trivial fix though.

Would this translation be used in vanilla?

You can get the string to appear with the following steps:

1. /npc create
2. /say @e[type=taterzens:npc]
3. Hover over the name of the created NPC. In this case, the output is [Player] Player (where Player is replaced with your in-game name). The first Player has a type of "Player" (entity.minecraft.player), while the second Player has a type of "entity.taterzens.npc".

Alternatively,

1. /npc create
2. /npc edit movement FREE
3. /npc edit behaviour HOSTILE
4. Let the Taterzen kill you.
5. Hover over the name of the killer in the death message. Notice that in the tooltip, it says "Type: entity.taterzens.npc"