Hi experts,
I tried to upload an xsd file to a message mapping. But i have an issue - Attribute reference 'http://www.w3.org/XML/1998/namespace#lang' is unresolved

Below is my xsd file. Any ideas would be appreciated.
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:import namespace="http://www.w3.org/XML/1998/namespace" schemaLocation="http://www.w3.org/2001/xml.xsd"/>
<xs:element name="catalog">
<xs:complexType>
<xs:sequence>
<xs:element name="header">
<xs:complexType>
<xs:sequence>
<xs:element name="image-settings">
<xs:complexType>
<xs:sequence>
<xs:element name="external-location">
<xs:complexType>
<xs:sequence>
<xs:element type="xs:anyURI" name="http-url"/>
<xs:element type="xs:string" name="https-url"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="view-types">
<xs:complexType>
<xs:sequence>
<xs:element type="xs:string" name="view-type" maxOccurs="unbounded" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element type="xs:string" name="variation-attribute-id"/>
<xs:element type="xs:string" name="alt-pattern"/>
<xs:element type="xs:string" name="title-pattern"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="product">
<xs:complexType>
<xs:sequence>
<xs:element type="xs:long" name="ean"/>
<xs:element type="xs:long" name="upc"/>
<xs:element type="xs:string" name="unit"/>
<xs:element type="xs:byte" name="min-order-quantity"/>
<xs:element type="xs:byte" name="step-quantity"/>
<xs:element name="display-name">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute ref="xml:lang"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element type="xs:string" name="store-force-price-flag"/>
<xs:element type="xs:string" name="store-non-inventory-flag"/>
<xs:element type="xs:string" name="store-non-revenue-flag"/>
<xs:element type="xs:string" name="store-non-discountable-flag"/>
<xs:element type="xs:string" name="online-flag"/>
<xs:element type="xs:string" name="available-flag"/>
<xs:element type="xs:string" name="searchable-flag"/>
<xs:element type="xs:string" name="page-attributes"/>
<xs:element name="custom-attributes">
<xs:complexType>
<xs:sequence>
<xs:element name="custom-attribute" maxOccurs="unbounded" minOccurs="0">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute type="xs:string" name="attribute-id" use="optional"/>
<xs:attribute ref="xml:lang"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element type="xs:string" name="pinterest-enabled-flag"/>
<xs:element type="xs:string" name="facebook-enabled-flag"/>
<xs:element name="store-attributes">
<xs:complexType>
<xs:sequence>
<xs:element type="xs:string" name="force-price-flag"/>
<xs:element type="xs:string" name="non-inventory-flag"/>
<xs:element type="xs:string" name="non-revenue-flag"/>
<xs:element type="xs:string" name="non-discountable-flag"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
<xs:attribute type="xs:int" name="product-id"/>
</xs:complexType>
</xs:element>
</xs:sequence>
<xs:attribute type="xs:string" name="catalog-id"/>
</xs:complexType>
</xs:element>
</xs:schema>