chore: Enable Korean (ko) (#1514)

config/locales/zh_CN.yml

@@ -16,7 +16,7 @@
 #'true': 'foo'
 #To learn more, please read the Rails Internationalization guide
 #available at https://guides.rubyonrails.org/i18n.html.
-zh-CN:
+zh_CN:
   hello: "您好世界"
   messages:
     reset_password_success: 哇！密码重置请求成功。请检查您的邮件获取说明。
@@ -27,6 +27,8 @@ zh-CN:
       invalid_email: 您输入了一个无效的电子邮件
       email_already_exists: "您已经注册了 %{email} 的帐户"
       failed: 注册失败
+  reports:
+    period: Reporting period %{since} to %{until}
   conversations:
     activity:
       status: