[FIX] contract: Invoice creation message translatable

As it was, the text to translate is not correctly extracted, so it's
not translated, creating a mix of languages, as `_creation_message`
is returning a translated sentence.

We take also the opportunity to change the way the sentence is built
for having as translatable only the "by contract" words, to avoid
possible errors in translations due to the placeholders.

contract/i18n/contract.pot

@@ -2334,6 +2334,13 @@ msgstr ""
 msgid "You must supply a date of next invoice for contract line '%s'"
 msgstr ""
 
+#. module: contract
+#. odoo-python
+#: code:addons/contract/models/contract.py:0
+#, python-format
+msgid "by contract"
+msgstr ""
+
 #. module: contract
 #: model_terms:ir.ui.view,arch_db:contract.contract_contract_form_view
 msgid "e.g. Contract XYZ"

contract/i18n/es.po

@@ -2543,6 +2543,13 @@ msgstr ""
 "Debe proporcionar la fecha de la próxima factura para la línea del contrato "
 "'%s'"
 
+#. module: contract
+#. odoo-python
+#: code:addons/contract/models/contract.py:0
+#, python-format
+msgid "by contract"
+msgstr "por el contrato"
+
 #. module: contract
 #: model_terms:ir.ui.view,arch_db:contract.contract_contract_form_view
 msgid "e.g. Contract XYZ"

contract/models/contract.py

@@ -619,17 +619,12 @@ def _invoice_followers(self, invoices):
     def _add_contract_origin(self, invoices):
         for item in self:
             for move in invoices & item._get_related_invoices():
+                translation = _("by contract")
                 move.message_post(
                     body=(
-                        _(
-                            (
-                                "%(msg)s by contract <a href=# data-oe-model=contract.contract"
-                                " data-oe-id=%(contract_id)d>%(contract)s</a>."
-                            ),
-                            msg=move._creation_message(),
-                            contract_id=item.id,
-                            contract=item.display_name,
-                        )
+                        f"{move._creation_message()} {translation} "
+                        f"<a href=# data-oe-model=contract.contract"
+                        f" data-oe-id={item.id}>{item.display_name}</a>."
                     )
                 )