[FIX] email_template: missing translations in email template

When composing an email based on an email template, some parts of the template
(the result of name_get on fields) were not translated.
This was due to missing language in context when rendering the template.
Fixes #3708, opw 617309
Merge branch '7.0' of https://github.com/odoo/odoo into 7.0-win32