function trimmed_post_title_shortcode($atts) {
    $atts = shortcode_atts(array(
        'post_id' => get_the_ID(),
        'length' => 80,
    ), $atts);

    $post_id = intval($atts['post_id']);
    if (!$post_id) {
        return '';
    }

    $title = get_the_title($post_id);
    if (mb_strlen($title) > $atts['length']) {
        $title = mb_substr($title, 0, $atts['length']) . '...';
    }

    return esc_html($title);
}
add_shortcode('trimmed_title', 'trimmed_post_title_shortcode');