i18n: update translations

translations/poexports/ja.json

@@ -516,7 +516,7 @@
     "DankSearch not available": "DankSearchが利用できません"
   },
   "Dark Mode": {
-    "Dark Mode": ""
+    "Dark Mode": "ダークモード"
   },
   "Date Format": {
     "Date Format": "日付形式"

translations/poexports/zh_CN.json

@@ -516,7 +516,7 @@
     "DankSearch not available": "DankSearch 不可用"
   },
   "Dark Mode": {
-    "Dark Mode": ""
+    "Dark Mode": "暗色模式"
   },
   "Date Format": {
     "Date Format": "日期格式"