Capture locale fr-FR and fr-CA In New Universal Login Experience

I’am using New Universal Login Experience Customize Login Page for my login screen of mobile app. i want to get full language code fr-FR / fr-CA based on my users device language selected. I’am trying to see if config object has any param which can give me full language code. but it is not there in Customize Login Page HTML.
var config = JSON.parse(decodeURIComponent(escape(window.atob(‘@@config@@’))));

Below is my code for login in production tenant and can not change my code. So without changing any code from SDK part is there any way I can get full locale code?

scope: constants.SCOPE,
audience: constants.AUDIENCE,
language: deviceLocale.split(‘-’)[0],
{ ephemeralSession: true },

Also how can I capture “locale” variable inside config object?