How to change navigator.userLanguage in IE11

Hello,

I am trying to change browser language to test my localization code, the way we detect locale is by JavaScript:

var userLang = navigator.userLanguage || navigator.language || navigator.browserLanguage || navigator.systemLanguage;

I tried the following ways + save, clear cache, restart browser, restart machine. After I made change, it still shows en, not the new lang I set, same behavior in win10, server08.

1. Tools -> Internet Option -> Language -> Language Preference, add new language and move to top.

2. change the Regions Options in the control panel and saved

Firefox and Chrome works great, so help needed fro IE11