diff --git a/addons/purchase/models/purchase.py b/addons/purchase/models/purchase.py
index 1dc8a09c23a..2b1acb20bd6 100644
--- a/addons/purchase/models/purchase.py
+++ b/addons/purchase/models/purchase.py
@@ -9,7 +9,7 @@ from odoo.osv import expression
 from odoo.tools import DEFAULT_SERVER_DATETIME_FORMAT
 from odoo.tools.float_utils import float_compare
 from odoo.exceptions import AccessError, UserError, ValidationError
-from odoo.tools.misc import formatLang
+from odoo.tools.misc import formatLang, get_lang
 
 
 class PurchaseOrder(models.Model):
@@ -638,7 +638,7 @@ class PurchaseOrderLine(models.Model):
 
         self.product_uom = self.product_id.uom_po_id or self.product_id.uom_id
         product_lang = self.product_id.with_context(
-            lang=self.partner_id.lang,
+            lang=get_lang(self.env, self.partner_id.lang).code,
             partner_id=self.partner_id.id,
             company_id=self.company_id.id,
         )
diff --git a/addons/sale/models/sale.py b/addons/sale/models/sale.py
index d9695f86a53..55a52d9d1f1 100644
--- a/addons/sale/models/sale.py
+++ b/addons/sale/models/sale.py
@@ -7,7 +7,7 @@ from itertools import groupby
 
 from odoo import api, fields, models, SUPERUSER_ID, _
 from odoo.exceptions import AccessError, UserError, ValidationError
-from odoo.tools.misc import formatLang
+from odoo.tools.misc import formatLang, get_lang
 from odoo.osv import expression
 from odoo.tools import float_is_zero, float_compare
 
@@ -1488,7 +1488,7 @@ class SaleOrderLine(models.Model):
             vals['product_uom_qty'] = self.product_uom_qty or 1.0
 
         product = self.product_id.with_context(
-            lang=self.order_id.partner_id.lang,
+            lang=get_lang(self.env, self.order_id.partner_id.lang).code,
             partner=self.order_id.partner_id,
             quantity=vals.get('product_uom_qty') or self.product_uom_qty,
             date=self.order_id.date_order,