The Salesforce tooling only supports a sub-set of the possible constructs available in WSDL/XSD. See SOAP Services: Defining a Class from a WSDL Document for the details.
One thing not supported is the external schema import your WSDL contains. That can potentially by manually fixed by you editing the files: grab the source of the imports and add themin-line. The example in the documentation of such a fix is to convert this:
<wsdl:types>
<xsd:schema
elementFormDefault="qualified"
targetNamespace="http://s3.amazonaws.com/doc/2006-03-01/">
<xsd:include schemaLocation="AmazonS3.xsd"/>
</xsd:schema>
</wsdl:types>
to this:
<wsdl:types>
<xsd:schema
xmlns:tns="http://s3.amazonaws.com/doc/2006-03-01/"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
targetNamespace="http://s3.amazonaws.com/doc/2006-03-01/">
<xsd:element name="CreateBucket">
<xsd:complexType>
<xsd:sequence>
[...]
</xsd:schema>
</wsdl:types>
Unfortunately your WSDL contains a lot of imports.
There is also a pretty hight chance that you will run into other unsupported features.