register custom taxonomy

add_action('init', function () {
    $tagLabels = [
        'name'                       => _x('Tagi', 'taxonomy general name'),
        'singular_name'              => _x('Tagi', 'taxonomy singular name'),
        'search_items'               => __('Search Tags'),
        'popular_items'              => __('Popular Tags'),
        'all_items'                  => __('All Tags'),
        'parent_item'                => null,
        'parent_item_colon'          => null,
        'edit_item'                  => __('Edit Tag'),
        'update_item'                => __('Update Tag'),
        'add_new_item'               => __('Add New Tag'),
        'new_item_name'              => __('New Tag Name'),
        'separate_items_with_commas' => __('Separate tags with commas'),
        'add_or_remove_items'        => __('Add or remove tags'),
        'choose_from_most_used'      => __('Choose from the most used tags'),
        'menu_name'                  => __('Tags'),
    ];
    register_taxonomy('small_ad_tag', ['page'], [
        'hierarchical'          => false,
        'labels'                => $tagLabels,
        'show_ui'               => true,
        'update_count_callback' => '_update_post_term_count',
        'query_var'             => true,
        'rewrite'               => ['slug' => 'small_ad_tag'],
    ]);
});