fix(Dunning): logic for fetching text (#43160)

erpnext/accounts/doctype/dunning/dunning.py

@@ -220,19 +220,31 @@ def get_linked_dunnings_as_per_state(sales_invoice, state):
 
 
 @frappe.whitelist()
-def get_dunning_letter_text(dunning_type, doc, language=None):
+def get_dunning_letter_text(dunning_type: str, doc: str | dict, language: str | None = None) -> dict:
+	DOCTYPE = "Dunning Letter Text"
+	FIELDS = ["body_text", "closing_text", "language"]
+
 	if isinstance(doc, str):
 		doc = json.loads(doc)
+
+	if not language:
+		language = doc.get("language")
+
 	if language:
-		filters = {"parent": dunning_type, "language": language}
-	else:
-		filters = {"parent": dunning_type, "is_default_language": 1}
-	letter_text = frappe.db.get_value(
-		"Dunning Letter Text", filters, ["body_text", "closing_text", "language"], as_dict=1
-	)
-	if letter_text:
-		return {
-			"body_text": frappe.render_template(letter_text.body_text, doc),
-			"closing_text": frappe.render_template(letter_text.closing_text, doc),
-			"language": letter_text.language,
-		}
+		letter_text = frappe.db.get_value(
+			DOCTYPE, {"parent": dunning_type, "language": language}, FIELDS, as_dict=1
+		)
+
+	if not letter_text:
+		letter_text = frappe.db.get_value(
+			DOCTYPE, {"parent": dunning_type, "is_default_language": 1}, FIELDS, as_dict=1
+		)
+
+	if not letter_text:
+		return {}
+
+	return {
+		"body_text": frappe.render_template(letter_text.body_text, doc),
+		"closing_text": frappe.render_template(letter_text.closing_text, doc),
+		"language": letter_text.language,
+	}