Update src/locales/ja/battle.json

Co-authored-by: Chapybara-jp <charlie.beer@hotmail.com>

src/locales/ja/battle.json

@@ -97,5 +97,5 @@
   "congratulations": "おめでとうございます！！",
   "beatModeFirstTime": "初めて　{{speciesName}}が　{{gameMode}}モードを　クリアした!\n{{newModifier}}を　手に入れた!",
   "ppReduced": "{{targetName}}の　{{moveName}}を　{{reduction}}削った!",
-  "mysteryEncounterAppeared": "What's this?"
+  "mysteryEncounterAppeared": "あれ？"
 }