"Elder Guardian Flops" showed as "Guardian Flops" in subtitles

subtitles.entity.elder_guardian.flop=Elder Guardian flops

is not used in game. Instead,

subtitles.entity.guardian.flop=Guardian flops

is used.

This is because there is no such sound event called

entity.elder_guardian.flop

and is not separated either in the sounds.json file. To fix this, simply add the sound event. Also, this should be added in the sounds.json file.

...
  "entity.elder_guardian.flop": {
    "sounds": [
      "mob/guardian/flop1",
      "mob/guardian/flop2",
      "mob/guardian/flop3",
      "mob/guardian/flop4"
    ],
    "subtitle": "subtitles.entity.elder_guardian.flop"
  },
...