To get all contract types you need to provide only the language code.

Query

<?xml version="1.0" encoding="UTF-8"?>
<envelope>
    <header>
        <actor>test</actor>
        <user>test</user>
        <password>test</password>
        <version>1.6.1</version>
        <timestamp>20030423170100</timestamp>
    </header>
    <query type="contract_types" product="hotel">
         <language code="it"/>
    </query>
</envelope>

Response

The response contains all contract types