// Total number of reviews for current product [count_reviews
add_shortcode('count_reviews', function() {
    $product_id = get_queried_object_id();

    if ( ! $product_id ) {
        return '';
    }

    $args = array(
        'post_type'      => 'simple-reviews',
        'post_status'    => 'publish',
        'posts_per_page' => -1,
        'meta_query'     => array(
            array(
                'key'     => 'review_post_id',
                'value'   => $product_id,
                'compare' => '=',
            ),
            array(
                'key'     => 'rating_review',
                'value'   => '',
                'compare' => '!=',
            ),
        ),
        'fields' => 'ids',
    );

    $query = new WP_Query($args);
    $total_reviews = count($query->posts);

    $label = plural_form($total_reviews, 'отзыв', 'отзыва', 'отзывов');

    return "{$total_reviews} {$label}";
});

// Функция склонения слов по числам
function plural_form($number, $form1, $form2, $form5) {
    $n = abs($number) % 100;
    $n1 = $n % 10;
    if ($n > 10 && $n < 20) return $form5;
    if ($n1 > 1 && $n1 < 5) return $form2;
    if ($n1 == 1) return $form1;
    return $form5;
}