diff --git a/searx/templates/oscar/base.html b/searx/templates/oscar/base.html
index 01dedc782..de7d05bf6 100644
--- a/searx/templates/oscar/base.html
+++ b/searx/templates/oscar/base.html
@@ -1,6 +1,6 @@
 {% from 'oscar/macros.html' import icon %}
 <!DOCTYPE html>
-<html lang="{{ preferences.get_value('locale') }}" xml:lang="{{ preferences.get_value('locale') }}"{% if rtl %} dir="rtl"{% endif %} class="nojs">
+<html lang="{{ locale_rfc5646 }}" xml:lang="{{ locale_rfc5646 }}"{% if rtl %} dir="rtl"{% endif %} class="nojs">
 <head>
     <meta charset="UTF-8" />
     <meta name="description" content="SearXNG - a privacy-respecting, hackable metasearch engine" />
diff --git a/searx/templates/simple/base.html b/searx/templates/simple/base.html
index ac6a09822..108d2fcf5 100644
--- a/searx/templates/simple/base.html
+++ b/searx/templates/simple/base.html
@@ -1,5 +1,5 @@
 <!DOCTYPE html>
-<html class="no-js" lang="en" {% if rtl %} dir="rtl"{% endif %}>
+<html class="no-js" lang="{{ locale_rfc5646 }}" {% if rtl %} dir="rtl"{% endif %}>
 <head>
   <meta charset="UTF-8" />
   <meta name="description" content="SearXNG — a privacy-respecting, hackable metasearch engine">
diff --git a/searx/webapp.py b/searx/webapp.py
index 61992c99f..85eb003a7 100755
--- a/searx/webapp.py
+++ b/searx/webapp.py
@@ -398,6 +398,11 @@ def _get_enable_categories(all_categories):
     return [x for x in all_categories if x in enabled_categories]
 
 
+def get_locale_rfc5646(locale):
+    parts = locale.split('_')
+    return parts[0].lower() + '-' + parts[-1].upper()
+
+
 def render(template_name, override_theme=None, **kwargs):
     # values from the HTTP requests
     kwargs['endpoint'] = 'results' if 'q' in kwargs else request.endpoint
@@ -420,6 +425,8 @@ def render(template_name, override_theme=None, **kwargs):
     kwargs['translations'] = json.dumps(get_translations(), separators=(',', ':'))
 
     locale = request.preferences.get_value('locale')
+    kwargs['locale_rfc5646'] = get_locale_rfc5646(locale)
+
     if locale in RTL_LOCALES and 'rtl' not in kwargs:
         kwargs['rtl'] = True
     if 'current_language' not in kwargs:
