Logging Persian messages with NLog

In my ASP.NET MVC project I have below config in Web.config as below:

 <configSections>
    <section name="nlog" type="NLog.Config.ConfigSectionHandler, NLog" />
  </configSections>
  <nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <targets>
      <target name="default" xsi:type="File" fileName="logs/app-log.txt" layout="
--------------------- ${level} (${longdate}) ----------------------$
IP: ${aspnet-request-ip}
Call Site: ${callsite}
${level} message: ${message}"/> archiveFileName="logs/archives/app-log.{#}.txt" archiveEvery="Day" archiveNumbering="Rolling" maxArchiveFiles="7" />
    </targets>
    <rules>
      <logger name="*" writeTo="default" />
    </rules>
  </nlog>

If my log message is in Persian text then in log file I have question mark as ????? instead of the Persian text.

How can I fix this problem? Any help will be appreciated!