$first_sentence = strtok($description, '.');  return $first_sentence . '.';

add_shortcode( 'product_description', 'display_product_description' );
function display_product_description( $atts ){    
    $atts = shortcode_atts( array(
        'id' => get_the_id(),
    ), $atts, 'product_description' );
    
    global $product;
    
    if ( ! is_a( $product, 'WC_Product') )
        $product = wc_get_product($atts['id']);
    
    $description = $product->get_description();
    
    $first_sentence = strtok($description, '.');
    
    return $first_sentence . '.';
}