使用您正在使用的代码，您将得到一个单词列表，这些单词是指向类别的链接。

您面临两个问题，一是添加分隔符，二是确保分隔符未添加到最后一项。

您有几个选项：使用代码：

$args = array(\'child_of\' => 3422 );
$categories = get_categories( $args );
$i = 1;
$separator = \', \'; // Include a separator to separate the category
$count_category = count($categories);   // get total category value  to limit the separator for last
foreach($categories as $category) { 
    if ($i != 1) {
       echo $separator;
    }
    if($i< $count_category && $i!=1){
      echo \'.\';
    }
    echo \'<a href="\' . get_category_link( $category->term_id ) . \'" title="\' . sprintf( __( "View all members in %s" ), $category->name ) . \'" \' . \'>\' . $category->name.\'</a> \';  
  $i++;
}

get_the_category_list( string $separator = \'\', string $parents = \'\', int $post_id = false )

$args = array(\'child_of\' => 3422 );
echo get_the_category_list (\',\' );