Fixed #25571 -- Fixed boolean evaluation of ungettext_lazy

django/utils/translation/__init__.py

@@ -107,6 +107,12 @@ def lazy_number(func, resultclass, number=None, **kwargs):
         proxy = lazy(func, resultclass)(**kwargs)
     else:
         class NumberAwareString(resultclass):
+            def __bool__(self):
+                return bool(kwargs['singular'])
+
+            def __nonzero__(self):  # Python 2 compatibility
+                return type(self).__bool__(self)
+
             def __mod__(self, rhs):
                 if isinstance(rhs, dict) and number:
                     try:

tests/i18n/tests.py

@@ -227,6 +227,10 @@ class TranslationTests(SimpleTestCase):
         )
         self.assertEqual(result % {'name': 'Joe', 'num': 4}, "Joe has 4 good results")
 
+    def test_ungettext_lazy_bool(self):
+        self.assertTrue(ungettext_lazy('%d good result', '%d good results'))
+        self.assertFalse(ungettext_lazy('', ''))
+
     @override_settings(LOCALE_PATHS=extended_locale_paths)
     def test_pgettext(self):
         trans_real._active = local()