[FIX] mail: fallback on English message

In case of bad translation that doesn't contain the placeholder

Context:
A bad Japanese translation was inserted

  #. module: mail
  #: code:addons/mail/models/mail_thread.py:0
  #, python-format
  msgid "Create new %(document)s"
  msgstr "新しい%(ドキュメント)を作成する"

The translation has been corrected but use the 14.0 syntax of _ method
to include placeholders and fallback on the English source term in
case of bad translation
cf odoo/odoo#52155

closes odoo/odoo#65517

Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>