wf_wp_content_excerpt

<?php
  
  /**
   * @description  Echoes custom the_excerpt from any post id. the_excerpt is 7 words long as default
   * 
   * @arguments mixed
   * @param array   $arguments     default NULL      array of arguments - the below mentioned + $limit 
   * @param int     $post_id       default NULL      the id of the post, if null, the current post is taken
   * @param string  $cut           default '...'     when nothing setted it will take the current Postcontent from loop and excerpt it
   */
  function sandbox_the_excerpt() {
    echo sandbox_get_the_excerpt($arguments);
  }

  /**
   * @description  Returns custom the_excerpt from any post id. the_excerpt is 7 words long as default
   * 
   * @arguments mixed
   * @param array   $arguments     default NULL      array of arguments - the below mentioned + $limit 
   * @param int     $post_id       default NULL      the id of the post, if null, the current post is taken
   * @param string  $cut           default '...'     when nothing setted it will take the current Postcontent from loop and excerpt it
   * 
   * @return string $the_excerpt
   */
  function sandbox_get_the_excerpt() {
        
    $defaults = array(
      'post_id' => NULL,
      'limit' => 7,
      'cut' => '...'
    );
    
    // Settings section
    if ( isset($arguments) && !empty($arguments) ) {
      if ( is_array($arguments) ) {
        
        // we get an array of arguments
        $settings = array_merge($defaults, $arguments[0]);
      } else {
        
        // apply default settings
        $settings = $defaults;

        $arguments = func_get_args();
        
        // apply single arguments
        foreach ( $args as $key => $value ) {
          if ( is_int($value) ) {
           $settings['post_id'] = $value;
          }
          if ( is_string($value) ) {
            $settings['cut'] = $value;
          }
        }     
      }
    }
    
    // get the post
    $post = get_post($settings['post_id']);
    
    // we need just the content
    $content = trim($post->post_content);
    
    // Apply Shortcodes
    $content = trim(do_shortcode($content));
    
    // prepare for word count
    $plain_content  = wp_strip_all_tags($content, true);
    $before_the_excerpt = explode(' ', $plain_content, $settings['limit']);
    
    if ( count($before_the_excerpt) >= $settings['limit'] ) {
      array_pop($before_the_excerpt);
    }
    
    $the_excerpt = implode(' ', $before_the_excerpt) . $settings['cut'];

    return $the_excerpt;
  }
  
?>

your code: _the_excerpt_of_cotent( null, 7, '...', false );
my code: _the_excerpt_of_cotent( false ); // i don not use $cut param

but you brought me to the idea to provide an array parameter to change the varibles and to not make use of func_get_args().

on line #16 you have to use do_shortcode, otherwise your content would not render the shortcodes. and your strip html function will not work for shortcodes only for html-tags. so therfore you translate first the shortcode to html to strip it and cut of the raw text without shortcodes and html.