Use HTTP Accept-Language to detect locale (#1166)

* Use HTTP Accept-Language to detect locale

* Fix gem order to comply with codeclimate

* Sort gem to comply with rubocop

* I18n.default_locale fallback when there is no accept-language header

app/controllers/concerns/localized.rb

@@ -26,6 +26,8 @@ module Localized
   end
 
   def default_locale
-    ENV.fetch('DEFAULT_LOCALE') { I18n.default_locale }
+    ENV.fetch('DEFAULT_LOCALE') { 
+      http_accept_language.compatible_language_from(I18n.available_locales) || I18n.default_locale
+    }
   end
 end