As I got answer from developers, for now it seems there is no direct way to translate these values. You can either use one language (translate whole header in a language you want), or create module that overrides default header. So this way you can put header information in rml report which can be translated. But the bad part is that you may need to create custom module for every report you want to translate, overriding default header.

I am facing same issue. If anyone know the solution. please post and close this question.

Same problem here. How to translate the name of the fields "Phone :", "Email :", "Website :" and "TIN :" in the footer?

Footer code:

<para style="main_footer">Phone : [[ company.partner_id.phone or '' ]] - Email : [[ company.partner_id.email or '' ]] - Website : [[ company.partner_id.website or '' ]] - TIN : [[ company.partner_id.vat or '' ]]</para>