To reproduce the bug: Go into multiplayer and select a server, then click Delete and the format error included with the message is prompted.
What should've happened: "(Server name here) will be lost forever! (A long time)
What happened: "'???????' Format error: '%s' will be lost forever! (A long time)
EDIT: I forgot to include that it would actually "'(Server name here)' Format error: '%s' will be lost forever! (A long time), in my case It was the message to confirm deletion of a server that I had named with ?'s.
MC-133587 Deleting server format error