feat: Thai language for every customization

- translations/th.csv: custom field labels, messages, print format and
  letter head text, the 22 Tax Withholding Category names; overrides the
  upstream Thai for the standard labels the print formats show
- print formats embed Sarabun (public/fonts, OFL) so PDFs render Thai on
  servers without a Thai font
- letter head labels go through _()
- withholding row description is translated when stored
- in_words: Thai "...บาทถ้วน" wording via num2words when the language is
  Thai (ThaiSalesInvoice.set_total_in_words); print formats re-derive it
  in the print language (get_in_words)
- fixture `modified` bumped so migrate re-imports the changed documents

default_thai_company/tax_withholding.py

@@ -10,6 +10,8 @@ from erpnext.accounts.doctype.tax_withholding_category.tax_withholding_category
 from frappe import _
 from frappe.utils import cint, flt
 
+from default_thai_company.utils import money_in_words
+
 # Liability: tax we withhold from suppliers and remit on P.N.D.3/53 (linked on every category).
 # Asset: tax customers withhold from us, creditable against corporate income tax.
 LIABILITY_ACCOUNT = "Withholding Tax Payable"
@@ -158,6 +160,17 @@ class ThaiSalesInvoice(SalesInvoice):
 				self.precision("amount_after_withholding"),
 			)
 
+	def set_total_in_words(self):
+		"""SellingController's version, with Thai wording when the saving user's
+		language is Thai. Print formats re-derive the text per print language
+		(`get_in_words`)."""
+		base_amount = abs(
+			self.base_grand_total if self.is_rounded_total_disabled() else self.base_rounded_total
+		)
+		self.base_in_words = money_in_words(base_amount, self.company_currency)
+		amount = abs(self.grand_total if self.is_rounded_total_disabled() else self.rounded_total)
+		self.in_words = money_in_words(amount, self.currency)
+
 
 class ThaiPaymentEntry(PaymentEntry):
 	def build_gl_map(self):
@@ -333,7 +346,8 @@ def get_customer_withholding(doc):
 		total += withholding_on(details_by_category[category], base_taxable, base_taxable, precision)
 
 	if len(details_by_category) == 1:
-		description = next(iter(details_by_category.values())).description
+		# category_name; translations/th.csv carries the fixture categories
+		description = _(next(iter(details_by_category.values())).description)
 	else:
 		description = _("Withholding tax deducted by customer")
 	return flt(total, precision), description