Explication
When /kill command executed the death messatge appears duplicated.
Replicate
Join single player word (cheats on)
Clear chat for better viewing (f3 + D)
Run command:
/kill
:info: The gamerules sendCommandFeedback and showDeathMessages must be activated.
Invalid. The top chat message is the translation of "Chilenderino was killed", the actual death message, while the bottom chat message is the translation of "Killed Chilenderino", the command feedback of /kill. If you want the two messages to be different in your language, then this is a language translation issue and you should refer to the official Minecraft translation project on Crowdin.