Should be easy to do
（查看法典：wp dropdown categories)
<h2><?php _e(\'Categories:\'); ?></h2>
<div>
<?php wp_dropdown_categories(\'show_option_all=ALL CATEGORIES&show_count=1&hierarchical=1\'); ?>
</div>
p.s如果要使用翻译进行包装，请按以下方式进行：
<h2><?php _e(\'Categories:\'); ?></h2>
<div>
<?php wp_dropdown_categories(\'show_option_all=\'.__(\'All Categories\', \'your_text_domain\').\'&show_count=1&hierarchical=1\'); ?>
</div>
