rewrite.php

<?php

add_filter('rewrite_rules_array', function ($rules) {
    $new_rules = [];
    $new_rules['^locations/(.+?)/(.+?)/(.+?)/?$'] = 'index.php?area=$matches[1]&area=$matches[2]&area=$matches[3]';
    $new_rules['^locations/(.+?)/(.+?)/(.+?)/?$'] = 'index.php?area=$matches[1]&area=$matches[2]&locations=$matches[3]';
    $new_rules['^locations/(.+?)/(.+?)/?$'] = 'index.php?area=$matches[1]&locations=$matches[2]';
    $new_rules['^locations/(.+?)/(.+?)/?$'] = 'index.php?area=$matches[1]&area=$matches[2]';
    $new_rules['^locations/(.+?)/?$'] = 'index.php?area=$matches[1]';

    return $new_rules + $rules;
});