Returns an associative array of timezone choices grouped by continent or context.

wp-get-timezone-choices.php

<?php

if ( ! function_exists( 'wp_util_get_timezone_choices' ) ) :

    /**
     * Returns an associative array of timezone choices grouped by continent or context.
     *
     * WordPress does not provide a static list of timezone choices or core function to return
     * an array of timezone choices that have been optionally translated and free from their
     * surrounding HTML markup as otherwise returned by WP core function wp_timezone_choice().
     *
     * @uses wp_timezone_choice()
     *
     * @param string $locale Optional. Locale to load the timezones in. Default current site locale.
     * @return array|bool Array of timezone choices grouped by continent or context, false otherwise.
     */
    function wp_util_get_timezone_choices( $locale = null ) {

        $timezones_choices = wp_timezone_choice( null, $locale );

        preg_match_all( '/(?:\<option value\=\")(.*)(?:\")/', $timezones_choices, $matches );
        
        if ( ! isset( $matches[1] ) ) {
            return false;
        }
        
        $timezones = array();

        foreach ( $matches[1] as $zone ) {
            $value = $label = $group = $zone;

            $zone = explode( '/', $zone );

            if ( count( $zone ) > 1 ) {
                $group = array_shift( $zone );
                $label = implode( ' - ', $zone );
            } elseif ( strpos( $value, 'UTC' ) !== false ) {
                $label = str_replace( array( '.25', '.5', '.75' ), array( ':15', ':30', ':45' ), $value );
                $group = 'UTC';
            }

            $timezones[ $group ][] = array(
                'value' => $value,
                'label' => $label,
            );
        }
        
        return $timezones;
        
    }

endif;