diff --git a/openedx/core/djangoapps/dark_lang/middleware.py b/openedx/core/djangoapps/dark_lang/middleware.py
index dd2e805166..07181a27df 100644
--- a/openedx/core/djangoapps/dark_lang/middleware.py
+++ b/openedx/core/djangoapps/dark_lang/middleware.py
@@ -16,6 +16,7 @@ from django.utils.deprecation import MiddlewareMixin
 
 from openedx.core.djangoapps.dark_lang import DARK_LANGUAGE_KEY
 from openedx.core.djangoapps.dark_lang.models import DarkLangConfig
+from openedx.core.djangoapps.site_configuration.helpers import get_value
 from openedx.core.djangoapps.user_api.preferences.api import get_user_preference
 
 # If django 1.7 or higher is used, the right-side can be updated with new-style codes.
@@ -90,8 +91,17 @@ class DarkLangMiddleware(MiddlewareMixin):
             return
 
         self._clean_accept_headers(request)
+        self._set_site_or_microsite_language(request)
         self._activate_preview_language(request)
 
+    def _set_site_or_microsite_language(self, request):
+        """
+        Apply language specified in site configuration.
+        """
+        language = get_value('LANGUAGE_CODE', None)
+        if language:
+            request.session[LANGUAGE_SESSION_KEY] = language
+
     def _fuzzy_match(self, lang_code):
         """Returns a fuzzy match for lang_code"""
         match = None
diff --git a/openedx/core/djangoapps/dark_lang/tests.py b/openedx/core/djangoapps/dark_lang/tests.py
index 170df89236..cfa5780110 100644
--- a/openedx/core/djangoapps/dark_lang/tests.py
+++ b/openedx/core/djangoapps/dark_lang/tests.py
@@ -13,6 +13,7 @@ from django.utils.translation import LANGUAGE_SESSION_KEY
 
 from openedx.core.djangoapps.dark_lang.middleware import DarkLangMiddleware
 from openedx.core.djangoapps.dark_lang.models import DarkLangConfig
+from openedx.core.djangoapps.site_configuration.tests.test_util import with_site_configuration
 from openedx.core.djangolib.testing.utils import CacheIsolationTestCase
 from common.djangoapps.student.tests.factories import UserFactory
 
@@ -256,6 +257,16 @@ class DarkLangMiddlewareTests(CacheIsolationTestCase):
         session[LANGUAGE_SESSION_KEY] = session_language
         session.save()
 
+    @with_site_configuration(configuration={'LANGUAGE_CODE': 'rel'})
+    def test_site_configuration_language(self):
+        # `LANGUAGE_CODE` in site configuration should override session lang
+        self._set_client_session_language('notrel')
+        self.client.get('/home')
+        self.assert_session_lang_equals(
+            'rel',
+            self.client.session
+        )
+
     def test_preview_lang_with_released_language(self):
         # Preview lang should always override selection
         self._post_set_preview_lang('rel')