I created a qweb report and it worked successfully. When I came to translate it I added this code:

<template id="my_report_id">
    <t t-call="report.html_container">
        <t t-foreach="doc_ids" t-as="doc_id">
        <t t-raw="translate_doc(doc_id, doc_model, 'lang' , 'my_module.my_report_id_document')"/>
        </t>
    </t>
</template>

When I tried to run it I got the following error 

QWebException: ""'my model name' object has no attribute 'lang'" while evaluating
'doc.lang'" while evaluating
"translate_doc(doc_id, doc_model, 'lang' , 'my_module.my_report_id_document')"

I changed it to several choices , for example:

'partner_id.lang'

user.lang

instance.session.user_context.lang, as per this link 

with no success. 

The module I'm working on I created it from scratch and it does not depend on any other module. How to resolve this issue.