diff --git a/app/controllers/concerns/localized.rb b/app/controllers/concerns/localized.rb
index 22bb5b21af..d9a7a7227b 100644
--- a/app/controllers/concerns/localized.rb
+++ b/app/controllers/concerns/localized.rb
@@ -27,7 +27,11 @@ module Localized
 
   def default_locale
     ENV.fetch('DEFAULT_LOCALE') {
-      http_accept_language.compatible_language_from(I18n.available_locales) || I18n.default_locale
+      user_supplied_locale || I18n.default_locale
     }
   end
+
+  def user_supplied_locale
+    http_accept_language.language_region_compatible_from(I18n.available_locales)
+  end
 end
diff --git a/spec/requests/localization_spec.rb b/spec/requests/localization_spec.rb
new file mode 100644
index 0000000000..d1b7bdc1da
--- /dev/null
+++ b/spec/requests/localization_spec.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe 'Localization' do
+  it 'uses a specific region when provided' do
+    headers = { 'Accept-Language' => 'zh-HK' }
+
+    get "/about", headers: headers
+    expect(response.body).to include(
+      I18n.t('about.about_mastodon', locale: 'zh-HK')
+    )
+  end
+
+  it 'falls back to a locale when region missing' do
+    headers = { 'Accept-Language' => 'es-FAKE' }
+
+    get "/about", headers: headers
+    expect(response.body).to include(
+      I18n.t('about.about_mastodon', locale: 'es')
+    )
+  end
+  it 'falls back to english when locale is missing' do
+    headers = { 'Accept-Language' => '12-FAKE' }
+
+    get "/about", headers: headers
+    expect(response.body).to include(
+      I18n.t('about.about_mastodon', locale: 'en')
+    )
+  end
+end