The bug
The hoverEvent messages "Invalid Entity!" and "Invalid Item!", which are used when the value for the action show_entity respectively show_item is invalid, are not translatable.
How to reproduce
Invalid Entity!
/tellraw @s {"text":"hover","hoverEvent":{"action":"show_entity","value":"{type:no quotation marks}"}}Invalid Item!
/tellraw @s {"text":"hover","hoverEvent":{"action":"show_item","value":"{id:invalid}"}}
Confirmed for 1.13.1.