diff --git a/odoo/addons/test_rpc/models.py b/odoo/addons/test_rpc/models.py
index 2d547a9947e..24b8e536708 100644
--- a/odoo/addons/test_rpc/models.py
+++ b/odoo/addons/test_rpc/models.py
@@ -18,3 +18,8 @@ class ModelB(models.Model):
     _description = "Model B"
 
     name = fields.Char(required=True)
+    value = fields.Integer()
+
+    _sql_constraints = [
+        ('qty_positive', 'check (value > 0)', 'The value must be positive'),
+    ]
diff --git a/odoo/addons/test_rpc/tests/test_error.py b/odoo/addons/test_rpc/tests/test_error.py
index e69a14b1d59..df32173781c 100644
--- a/odoo/addons/test_rpc/tests/test_error.py
+++ b/odoo/addons/test_rpc/tests/test_error.py
@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 
 from functools import partial
+from xmlrpc.client import Fault
 
 from odoo.tests import common, tagged
 from odoo.tools.misc import mute_logger
@@ -65,3 +66,8 @@ class TestError(common.HttpCase):
             )
             self.assertIn("Model: Model A (test_rpc.model_a)", e.faultString)
             self.assertIn("Constraint: test_rpc_model_a_field_b2_fkey", e.faultString)
+
+    def test_03_sql_constraint(self):
+        with mute_logger("odoo.sql_db"):
+            with self.assertRaisesRegex(Fault, r'The operation cannot be completed: The value must be positive'):
+                self.rpc("test_rpc.model_b", "create", {"name": "B1", "value": -1})
diff --git a/odoo/service/model.py b/odoo/service/model.py
index c31a14977d5..a4b46f96016 100644
--- a/odoo/service/model.py
+++ b/odoo/service/model.py
@@ -109,7 +109,7 @@ def _as_validation_error(env, exc):
     if exc.diag.constraint_name in env.registry._sql_constraints:
         return ValidationError(_(
             "The operation cannot be completed: %s",
-            translate_sql_constraint(env.cr, exc.diag.constraint_name, env.context['lang'])
+            translate_sql_constraint(env.cr, exc.diag.constraint_name, env.context.get('lang', 'en_US'))
         ))
 
     return ValidationError(_("The operation cannot be completed: %s", exc.args[0]))