🐛(i18n) add back the missing email translations

We changed the way we upload the translations to
Crowdin, some translations were missing for the
email templates. We add them back and improve
the tests to make sure we don't forget them again.

src/backend/core/tests/documents/test_api_document_invitations.py

@@ -458,6 +458,10 @@ def test_api_document_invitations_create_email_from_content_language():
 
     email_content = " ".join(email.body.split())
     assert f"{user.full_name} a partagé un document avec vous!" in email_content
+    assert (
+        "Docs, votre nouvel outil incontournable pour organiser, partager et collaborer "
+        "sur vos documents en équipe." in email_content
+    )
 
 
 def test_api_document_invitations_create_email_from_content_language_not_supported():