Source: polyfill/Intl/bcp47.js

// Licensed Materials - Property of IBM
//
// IBM Watson Analytics
//
// (C) Copyright IBM Corp. 2018
//
// US Government Users Restricted Rights - Use, duplication or
// disclosure restricted by GSA ADP Schedule Contract with IBM Corp.

( function( exports, ObjectPolyfill )
{
"use strict";

// Instead of fully validating the tag, we match any string that starts with two or three [a-z] characters,
// followed by any number of -[a-z0-9] suffixes.
var reTag = /^(i|[a-zA-Z]{2,3})((?:\-[a-zA-Z0-9]+)*)$/;

var reFormat = /^[a-zA-Z]+|\-\w+/g;

function bcp47Replace( _match, _offset )
{
    /*
     * Formatting follows simple rules:
     *  > if NOT the first entry
     *      > Length 2: UPPER case
     *      > Length 4: Title case
     *  > lower case
     * For any match that is not the first (_offset is 0), take into account '-' is in the match
     */
    var len = _offset ? _match.length : 0;
    return len === 3 ? // +1 for '-'
        _match.toUpperCase() :
        len === 5 ? // +1 for '-'
            _match.substr( 0, 2 ).toUpperCase() + _match.substr( 2 ).toLowerCase() :
            _match.toLowerCase();
}

function isStructurallyValidLanguageTag( _tag )
{
    // With the current implementation, the type check for string is unnecessary.
    return /*typeof _tag === "string" &&*/ reTag.test( _tag );
}

function canonicalizeLanguageTag( _tag )
{
    // Officially this validation should be performed before calling this function,
    // but with this limited implementation it's more convenient to perform it here.
    var tag = String( _tag );
    if ( !isStructurallyValidLanguageTag( tag ) )
        throw new RangeError( "Invalid language tag: " + tag );
    return tag.replace( reFormat, bcp47Replace );
}

/**
 * @memberof module:barejs/polyfill/Intl
 * @param {String|Array} _locales
 * @return {String[]} List of canonical locale tags.
 */
exports.getCanonicalLocales = function getCanonicalLocales( _locales )
{
    var seen;

    if ( _locales === undefined )
    {
        seen = new Array( 0 );
    }
    else if ( typeof _locales === "string" )
    {
        seen = new Array( 1 );
        seen[ 0 ] = canonicalizeLanguageTag( _locales );
    }
    else
    {
        seen = [];
        var locales = ObjectPolyfill.toObject( _locales );
        var len = locales.length || 0;
        for ( var i = 0; i < len; ++i )
        {
            var tag = canonicalizeLanguageTag( locales[ i ] );
            if ( seen.indexOf( tag ) < 0 )
                seen.push( tag );
        }
    }

    return seen;
};

}( module.exports, require( "../Object" ) ) );