diff --git a/odoo/addons/base/models/ir_http.py b/odoo/addons/base/models/ir_http.py
index b89a846110b..1dbb94cca5b 100644
--- a/odoo/addons/base/models/ir_http.py
+++ b/odoo/addons/base/models/ir_http.py
@@ -29,7 +29,7 @@ from odoo.exceptions import AccessDenied, AccessError, MissingError
 from odoo.http import request, Response, ROUTING_KEYS, Stream
 from odoo.modules.registry import Registry
 from odoo.service import security
-from odoo.tools import consteq, submap
+from odoo.tools import get_lang, submap
 from odoo.tools.translate import code_translations
 from odoo.modules.module import get_resource_path, get_module_path
 
@@ -144,6 +144,11 @@ class IrHttp(models.AbstractModel):
             if isinstance(val, models.BaseModel) and isinstance(val._uid, RequestUID):
                 args[key] = val.with_user(request.env.uid)
 
+        # verify the default language set in the context is valid,
+        # otherwise fallback on the company lang, english or the first
+        # lang installed
+        request.update_context(lang=get_lang(request.env)._get_cached('code'))
+
     @classmethod
     def _dispatch(cls, endpoint):
         result = endpoint(**request.params)
diff --git a/odoo/addons/test_http/controllers.py b/odoo/addons/test_http/controllers.py
index 242174ab1bc..9933c0862f6 100644
--- a/odoo/addons/test_http/controllers.py
+++ b/odoo/addons/test_http/controllers.py
@@ -67,6 +67,10 @@ class TestHttp(http.Controller):
     def echo_http_csrf(self, **kwargs):
         return str(kwargs)
 
+    @http.route('/test_http/echo-http-context-lang', type='http', auth='public', methods=['GET'], csrf=False)
+    def echo_http_context_lang(self, **kwargs):
+        return request.env.context.get('lang', '')
+
     @http.route('/test_http/echo-json', type='json', auth='none', methods=['POST'], csrf=False)
     def echo_json(self, **kwargs):
         return kwargs
diff --git a/odoo/addons/test_http/tests/test_session.py b/odoo/addons/test_http/tests/test_session.py
index 6a0ea900745..647dc744a8c 100644
--- a/odoo/addons/test_http/tests/test_session.py
+++ b/odoo/addons/test_http/tests/test_session.py
@@ -88,3 +88,46 @@ class TestHttpSession(TestHttpBase):
         res = self.multidb_url_open('/test_http/greeting-user')
         res.raise_for_status()
         self.assertEqual(res.status_code, 200, "Should not be redirected to /web/login")
+
+    def test_session5_default_lang(self):
+        self.env['res.lang']._activate_lang('en_US')  # default lang
+        lang_fr = self.env['res.lang']._activate_lang('fr_FR')
+
+        with self.subTest(case='no preferred lang'):
+            res = self.url_open('/test_http/echo-http-context-lang')
+            self.assertEqual(res.text, 'en_US')
+
+        with self.subTest(case='fr preferred and fr_FR enabled'):
+            res = self.url_open('/test_http/echo-http-context-lang', headers={
+                'Accept-Language': 'fr',
+            })
+            self.assertEqual(res.text, 'fr_FR')
+
+        with self.subTest(case='fr preferred but fr_FR disabled'):
+            lang_fr.active = False
+            res = self.url_open('/test_http/echo-http-context-lang', headers={
+                'Accept-Language': 'fr',
+            })
+            self.assertEqual(res.text, 'en_US')
+
+    def test_session6_saved_lang(self):
+        session = self.authenticate('demo', 'demo')
+        self.env['res.lang']._activate_lang('en_US')  # default lang
+        lang_fr = self.env['res.lang']._activate_lang('fr_FR')
+
+        with self.subTest(case='no saved lang'):
+            res = self.url_open('/test_http/echo-http-context-lang')
+            self.assertEqual(res.text, 'en_US')
+
+        with self.subTest(case='fr saved and fr_FR enabled'):
+            session.context['lang'] = 'fr_FR'
+            odoo.http.root.session_store.save(session)
+            res = self.url_open('/test_http/echo-http-context-lang')
+            self.assertEqual(res.text, 'fr_FR')
+
+        with self.subTest(case='fr saved but fr_FR disabled'):
+            session['lang'] = 'fr_FR'
+            odoo.http.root.session_store.save(session)
+            lang_fr.active = False
+            res = self.url_open('/test_http/echo-http-context-lang')
+            self.assertEqual(res.text, 'en_US')
diff --git a/odoo/tools/misc.py b/odoo/tools/misc.py
index 3b2b0b95656..979ea936cbf 100644
--- a/odoo/tools/misc.py
+++ b/odoo/tools/misc.py
@@ -1312,14 +1312,14 @@ def get_lang(env, lang_code=False):
     """
     Retrieve the first lang object installed, by checking the parameter lang_code,
     the context and then the company. If no lang is installed from those variables,
-    fallback on the first lang installed in the system.
+    fallback on english or on the first lang installed in the system.
 
     :param env:
     :param str lang_code: the locale (i.e. en_US)
     :return res.lang: the first lang found that is installed on the system.
     """
     langs = [code for code, _ in env['res.lang'].get_installed()]
-    lang = langs[0]
+    lang = 'en_US' if 'en_US' in langs else langs[0]
     if lang_code and lang_code in langs:
         lang = lang_code
     elif env.context.get('lang') in langs: