I'm trying to translate the default name for Purchase Order (in purchase order creation form) from "New" to "NEU" (English to German), I tried to do that in a new module and i included the purchase module in the manifest file .

The translation should work when i update my module , however it does not work.

I tried this 

#. module: purchase
#: code:addons/purchase/models/purchase.py:77
#: code:addons/purchase/models/purchase.py:158
#, python-format
msgid "New"
msgstr "Neu"

#. module: purchase
#:model:ir.model.fields,field_description:purchase.field_purchase_order__default_name
msgid "New"
msgstr "Neu"

NOTE : I have already installed German language and i'm already using it, most of the translation terms are working except this one.
any solution ??