WordPress locale to PHP & jQuery date formats

<?php
/**
 * Determines the correct date format for the current WordPress locale.
 *
 * This function makes it extremely easy to keep PHP date formatting and
 * jQuery datepicker identical. It retrieves the correct date format based
 * on offical ICU formatting, bypassing the need for the PHP Intl module.
 *
 * @uses   wp-locale-to-date-format.json
 * @see    https://pastebin.com/eT3ku5fR
 *
 * @param  string $length short|full
 * @param  string $script Optional. Either php or jquery. Defaults to php.
 * @return string
 */
function stonehenge_localize_date_format( $length, $script = 'php' ) {
    $locale = str_replace( '_formal', '', determine_locale() ); // Dates are neither formal nor informal.
    $json   = file_get_contents( __DIR__ . '/assets/wp-locale-to-date-format.json' );
    $source = json_decode( $json, true );

    return array_key_exists( $locale, $source ) ? $source[ $locale ][ $script ][ $length ] : ( 'php' === $script ? 'Y-m-d' : 'yy-mm-dd' );
}

/**
 * Returns the localized date by the given formatting type.
 *
 * Prevents errors by checking if the supplied input is numeric.
 *
 * Example:
 * `echo stonehenge_localize_date( $value );`           => 27-08-2024 (d-m-Y)
 * `echo stonehenge_localize_date( $value, 'full' );`   => dinsdag 27 augustus 2024 (l j F Y)
 *
 * @param  string $date   Any (un)formatted date string.
 * @param  string $length Optional. The short of full date format. Defaults to short.
 * @return string
 */
function stonehenge_localize_date( $date, $length = 'short' ) {
    $date   = is_numeric( $date ) ? $date : strtotime( $date );  // Prevent errors.
    $format = stonehenge_localize_date_format( 'php', $length );

    return date_i18n( $format, $date );
}

/**
 * Returns localized values for the jQuery UI datepicker using the WP_Locale globals.
 *
 * This function removes the need for any third-party translation files and prevents incorrect
 * date format processing by the function `wp_localize_jquery_ui_datepicker`.
 *
 * @global WP_Locale $wp_locale WordPress date and time locale object.
 * @return array
 */
function stonehenge_localize_datepicker() {
    global $weekday, $weekday_abbrev, $month, $month_abbrev;

    // Correct the WP_Locale globals as most languages only use lowercase mid sentence.
    return array(
        'date_format'   => esc_attr( stonehenge_localize_date_format( 'short', 'jquery' ) ),
        'days_full'     => array_map( 'ucfirst', $weekday ),
        'days_short'    => array_map( 'ucfirst', $weekday_abbrev ),
        'months_full'   => array_map( 'ucfirst', $month ),
        'months_short'  => array_map( 'ucfirst', $month_abbrev ),
        'first_day'     => absint( get_option( 'start_of_week' ) ),
        'next'          => esc_attr__( 'Next' ),
        'previous'      => esc_attr__( 'Previous' ),
        'close'         => esc_attr__( 'Close' ),
        'today'         => esc_attr__( 'Today' )
    );
}

/**
 * Use wp_localize_script() to send the localized jQuery date picker options.
 */
wp_localize_script( 'your-script-handle', 'object', stonehenge_localize_datepicker() );

/**
 * Call the localized values in your script.js
 */
jQuery(document).ready( function($) {
    $.datepicker({
        dateFormat: object.date_format,         // dd-mm-yy
        dayNames: object.days_full,             // Zondag, Maandag, Dinsdag, Woensdag ...
        dayNamesShort: object.days_short,       // Zo, Ma, Di, Wo ...
        monthNames: object.months_full,         // Januari, Februari, Maart, April ...
        monthNamesShort: object.months_short,   // Jan, Feb, Maa, Apr ...
        firstDay: object.first_day,             // 1 (Monday)
        prevText: object.previous,              // Vorige
        nextText: object.next,                  // Volgende
        currentText: object.today,              // Vandaag
        yearRange: "-1:+4",                     // 2023 - 2028
        changeMonth: true,
        changeYear: true
    });
});