/home/your-username/.config/xfce4/xfconf/xfce-perchannel-xml

<?xml version="1.0" encoding="UTF-8"?>

<channel name="keyboard-layout" version="1.0">
  <property name="Default" type="empty">
    <property name="XkbDisable" type="bool" value="false"/>
    <property name="XkbLayout" type="string" value="us,fr,ro"/>
    <property name="XkbVariant" type="string" value=",,std"/>
  </property>
</channel>