How to store localization in seesion or cookie

I am developing a multi language app in ci4 i have done fully with the en version and i try to translate to fr so when i use route method to push the lang to the url e.g http://site.com/en/page it broken my app because the en is detected the $this->request->uri->getSegment()1;

This method will crash my app because there is a login used in the app using the getSegment method so i was think if the is a way to store the supported lang in session or cookie.

Thanks.