"instrument.unregistered_sadface" is untranslated and displays as its raw string instead.
How to reproduce:
Use the command:
/give @s goat_horn
Look at the item you are given in your inventory.
"instrument.unregistered_sadface" is untranslated and displays as its raw string instead.
How to reproduce:
Use the command: /give @s goat_horn
Look at the item you are given in your inventory.
I can confirm this behavior.