How to reproduce:
Grab a fishing rod
Cast your fishing rod
Type this command in chat:
/say @e[type=fishing_bobber]
It'll show [PLAYERNAME] entity.minecraft.fishing_bobber instead of the translated version
This can easily be fixed by adding this to the lang file:
"entity.minecraft.fishing_bobber": "Fishing Bobber"
This can be marked as fixed for 18w06a