chore: rewrite user-facing messages in Regional module

Conservative cleanup of frappe.throw/msgprint messages per the message style
guide; meaning, severity, and .format() arguments are unchanged:

- index bare {} placeholders as {0}/{1}/... so translators can reorder
- move f-strings / .format() / concatenation out of _() (they break gettext
  extraction and never translate)
- wrap translatable dynamic values (DocType/Select labels) in _()
- fix grammar and colloquialisms
- drop no-op _() wrapping runtime-built strings

Part of #53976.

erpnext/regional/doctype/import_supplier_invoice/import_supplier_invoice.py

@@ -85,7 +85,7 @@ class ImportSupplierInvoice(Document):
 			}
 
 			if not invoices_args.get("bill_no", ""):
-				frappe.throw(_("Numero has not set in the XML file"))
+				frappe.throw(_("Numero has not been set in the XML file"))
 
 			supp_dict = get_supplier_details(file_content)
 			invoices_args["destination_code"] = get_destination_code_from_file(file_content)

erpnext/regional/italy/utils.py

@@ -224,7 +224,7 @@ def sales_invoice_validate(doc):
 
 	if not doc.company_address:
 		frappe.throw(
-			_("Please set an Address on the Company '%s'" % doc.company),
+			_("Please set an Address on the Company '{0}'").format(doc.company),
 			title=_("E-Invoicing Information Missing"),
 		)
 	else:
@@ -254,7 +254,7 @@ def sales_invoice_validate(doc):
 		doc.customer_fiscal_code = customer.fiscal_code
 		if not doc.customer_fiscal_code:
 			frappe.throw(
-				_("Please set Fiscal Code for the customer '%s'" % doc.customer),
+				_("Please set Fiscal Code for the customer '{0}'").format(doc.customer),
 				title=_("E-Invoicing Information Missing"),
 			)
 	else:
@@ -262,14 +262,14 @@ def sales_invoice_validate(doc):
 			doc.customer_fiscal_code = customer.fiscal_code
 			if not doc.customer_fiscal_code:
 				frappe.throw(
-					_("Please set Fiscal Code for the public administration '%s'" % doc.customer),
+					_("Please set Fiscal Code for the public administration '{0}'").format(doc.customer),
 					title=_("E-Invoicing Information Missing"),
 				)
 		else:
 			doc.tax_id = customer.tax_id
 			if not doc.tax_id:
 				frappe.throw(
-					_("Please set Tax ID for the customer '%s'" % doc.customer),
+					_("Please set Tax ID for the customer '{0}'").format(doc.customer),
 					title=_("E-Invoicing Information Missing"),
 				)