Fix locales again (#3010)

* Normalize locales

* Restore "mention" locale key

app/javascript/mastodon/locales/zh-HK.json

@@ -88,6 +88,7 @@
   "navigation_bar.public_timeline": "跨站時間軸",
   "notification.favourite": "{name} 喜歡你的文章",
   "notification.follow": "{name} 開始關注你",
+  "notification.mention": "{name} 提及你",
   "notification.reblog": "{name} 轉推你的文章",
   "notifications.clear": "清空通知紀錄",
   "notifications.clear_confirmation": "你確定要清空通知紀錄嗎？",