refactor(stock-balance): reduce alt UOM to single column, fix i18n, add tests

- Reduce from 2 alternate UOM columns to 1 (first alt UOM by idx)
- Fix broken translation strings: replace _(f"...{slot}") with
  _("...") — f-strings inside _() are never extracted by bench
  get-untranslated, breaking non-English installations
- Simplify fieldnames: alt_uom_1/alt_uom_1_bal_qty → alt_uom/alt_uom_bal_qty
- Add 4 test cases covering: single alt UOM, no alt UOM, disabled filter,
  and multiple alt UOMs (first-wins behaviour)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
(cherry picked from commit 021b807057)

erpnext/stock/report/stock_balance/stock_balance.py

@@ -605,7 +605,7 @@ class StockBalanceReport:
 		add_additional_uom_columns(self.columns, self.data, self.filters.include_uom, conversion_factors)
 
 	def add_alt_uom_columns(self) -> None:
-		"""Add up to 2 alternate UOM balance columns per item after the Balance Qty column."""
+		"""Add an alternate UOM balance column after the Balance Qty column."""
 		if not self.filters.get("show_alt_uom_balance"):
 			return
 
@@ -613,7 +613,6 @@ class StockBalanceReport:
 		if not item_alt_uom_map:
 			return
 
-		# Insert columns right after bal_qty (in reverse order so slot 1 comes first)
 		bal_qty_idx = next(
 			(i for i, col in enumerate(self.columns) if isinstance(col, dict) and col.get("fieldname") == "bal_qty"),
 			None,
@@ -621,37 +620,35 @@ class StockBalanceReport:
 		if bal_qty_idx is None:
 			return
 
-		for slot in (2, 1):
-			self.columns.insert(
-				bal_qty_idx + 1,
-				{
-					"label": _(f"Balance Qty (Alt UOM {slot})"),
-					"fieldname": f"alt_uom_{slot}_bal_qty",
-					"fieldtype": "Float",
-					"width": 140,
-				},
-			)
-			self.columns.insert(
-				bal_qty_idx + 1,
-				{
-					"label": _(f"Alt UOM {slot}"),
-					"fieldname": f"alt_uom_{slot}",
-					"fieldtype": "Data",
-					"width": 90,
-				},
-			)
+		# Insert in reverse so "Alt UOM" name column appears before qty column
+		self.columns.insert(
+			bal_qty_idx + 1,
+			{
+				"label": _("Balance Qty (Alt UOM)"),
+				"fieldname": "alt_uom_bal_qty",
+				"fieldtype": "Float",
+				"width": 140,
+			},
+		)
+		self.columns.insert(
+			bal_qty_idx + 1,
+			{
+				"label": _("Alt UOM"),
+				"fieldname": "alt_uom",
+				"fieldtype": "Data",
+				"width": 90,
+			},
+		)
 
 		for row in self.data:
 			alt_uoms = item_alt_uom_map.get(row.item_code, [])
-			for slot in (1, 2):
-				idx = slot - 1
-				if idx < len(alt_uoms):
-					uom, factor = alt_uoms[idx]["uom"], flt(alt_uoms[idx]["conversion_factor"])
-					row[f"alt_uom_{slot}"] = uom
-					row[f"alt_uom_{slot}_bal_qty"] = flt(row.get("bal_qty", 0)) / factor if factor else 0.0
-				else:
-					row[f"alt_uom_{slot}"] = ""
-					row[f"alt_uom_{slot}_bal_qty"] = 0.0
+			if alt_uoms:
+				uom, factor = alt_uoms[0]["uom"], flt(alt_uoms[0]["conversion_factor"])
+				row["alt_uom"] = uom
+				row["alt_uom_bal_qty"] = flt(row.get("bal_qty", 0)) / factor if factor else 0.0
+			else:
+				row["alt_uom"] = ""
+				row["alt_uom_bal_qty"] = 0.0
 
 	def get_item_alt_uom_map(self) -> dict:
 		"""Return {item_code: [{uom, conversion_factor}, ...]} for alternate UOMs (excluding stock UOM)."""
@@ -679,7 +676,7 @@ class StockBalanceReport:
 		result: dict = {}
 		for row in rows:
 			result.setdefault(row.parent, [])
-			if len(result[row.parent]) < 2:  # keep up to 2 alternate UOMs
+			if not result[row.parent]:  # keep only the first alternate UOM (lowest idx)
 				result[row.parent].append({"uom": row.uom, "conversion_factor": row.conversion_factor})
 
 		return result

erpnext/stock/report/stock_balance/test_stock_balance.py

@@ -167,6 +167,52 @@ class TestStockBalance(ERPNextTestSuite):
 		self.assertPartialDictEq(attributes, rows[0])
 		self.assertInvariants(rows)
 
+	def test_alt_uom_balance_single_uom(self):
+		"""Alt UOM columns show correct name and converted qty for an item with one alternate UOM."""
+		self.item.append("uoms", {"conversion_factor": 12, "uom": "Box"})
+		self.item.save()
+
+		self.generate_stock_ledger(self.item.name, [_dict(qty=24, rate=10)])
+
+		rows = stock_balance(self.filters.update({"show_alt_uom_balance": 1}))
+		self.assertEqual(len(rows), 1)
+		self.assertEqual(rows[0].get("alt_uom"), "Box")
+		self.assertAlmostEqual(rows[0].get("alt_uom_bal_qty"), 2.0)  # 24 / 12
+
+	def test_alt_uom_balance_no_alternate_uom(self):
+		"""Alt UOM columns are not added when no items in the report have alt UOMs."""
+		self.generate_stock_ledger(self.item.name, [_dict(qty=5, rate=10)])
+
+		columns, _ = execute(self.filters.update({"show_alt_uom_balance": 1}))
+		col_fieldnames = [c.get("fieldname") for c in columns if isinstance(c, dict)]
+		self.assertNotIn("alt_uom", col_fieldnames)
+		self.assertNotIn("alt_uom_bal_qty", col_fieldnames)
+
+	def test_alt_uom_balance_filter_disabled(self):
+		"""No alt UOM columns are injected when show_alt_uom_balance is not set."""
+		self.item.append("uoms", {"conversion_factor": 12, "uom": "Box"})
+		self.item.save()
+
+		self.generate_stock_ledger(self.item.name, [_dict(qty=24, rate=10)])
+
+		columns, _ = execute(self.filters)
+		col_fieldnames = [c.get("fieldname") for c in columns if isinstance(c, dict)]
+		self.assertNotIn("alt_uom", col_fieldnames)
+		self.assertNotIn("alt_uom_bal_qty", col_fieldnames)
+
+	def test_alt_uom_balance_uses_first_alternate_uom(self):
+		"""When an item has multiple alt UOMs, only the first (lowest idx) is shown."""
+		self.item.append("uoms", {"conversion_factor": 12, "uom": "Box"})
+		self.item.append("uoms", {"conversion_factor": 144, "uom": "Carton"})
+		self.item.save()
+
+		self.generate_stock_ledger(self.item.name, [_dict(qty=144, rate=10)])
+
+		rows = stock_balance(self.filters.update({"show_alt_uom_balance": 1}))
+		self.assertEqual(len(rows), 1)
+		self.assertEqual(rows[0].get("alt_uom"), "Box")
+		self.assertAlmostEqual(rows[0].get("alt_uom_bal_qty"), 12.0)  # 144 / 12, not 144 / 144
+
 	def test_stock_ageing_data_accepts_batchwise_valuation_slots(self):
 		fifo_queue = [
 			["SA-BATCH-NEWER", 1, 2.0, "2021-12-05", 20.0],