custom taxonomy create.

custom taxonomy

// Register Custom Taxonomy
function news_custom_taxonomy() {

	$labels = array(
		'name'                       => _x( 'ニュースカテゴリ', 'Taxonomy General Name', 'text_domain' ),
		'singular_name'              => _x( 'ニュースカテゴリ', 'Taxonomy Singular Name', 'text_domain' ),
		'menu_name'                  => __( 'ニュースカテゴリ', 'text_domain' ),
		'all_items'                  => __( 'すべてのニュースカテゴリ', 'text_domain' ),
		'parent_item'                => __( '親カテゴリ', 'text_domain' ),
		'parent_item_colon'          => __( '親カテゴリ:', 'text_domain' ),
		'new_item_name'              => __( '新しいカテゴリ', 'text_domain' ),
		'add_new_item'               => __( '新しいカテゴリを追加', 'text_domain' ),
		'edit_item'                  => __( 'カテゴリを編集', 'text_domain' ),
		'update_item'                => __( 'カテゴリを更新', 'text_domain' ),
		'separate_items_with_commas' => __( 'アイテムをカンマで区切る', 'text_domain' ),
		'search_items'               => __( 'カテゴリを検索', 'text_domain' ),
		'add_or_remove_items'        => __( '追加、または削除', 'text_domain' ),
		'choose_from_most_used'      => __( 'Choose from the most used items', 'text_domain' ),
		'not_found'                  => __( '見つかりませんでした。', 'text_domain' ),
	);
	$args = array(
		'labels'                     => $labels,
		'hierarchical'               => false,
		'public'                     => true,
		'show_ui'                    => true,
		'show_admin_column'          => true,
		'show_in_nav_menus'          => true,
		'show_tagcloud'              => true,
	);
	register_taxonomy( 'news_category', array( 'news' ), $args );

}

// Hook into the 'init' action
add_action( 'init', 'news_custom_taxonomy', 0 );

You can create custom taxonomy in WordPress using this simple code in functions.php

add_action( 'init', 'create_cw_hierarchical_taxonomy', 0 );
//create a custom taxonomy name
function create_cw_hierarchical_taxonomy() {
$labels = array(
'name' => _x( 'Topics', 'taxonomy general name' ),
'singular_name' => _x( 'Topic', 'taxonomy singular name' ),
'search_items' => __( 'Search Topics' ),
'all_items' => __( 'All Topics' ),
'parent_item' => __( 'Parent Topic' ),
'parent_item_colon' => __( 'Parent Topic:' ),
'edit_item' => __( 'Edit Topic' ),
'update_item' => __( 'Update Topic' ),
'add_new_item' => __( 'Add New Topic' ),
'new_item_name' => __( 'New Topic Name' ),
'menu_name' => __( 'Topics' ),
);
// taxonomy register
register_taxonomy('topics',array('post'), array(
'hierarchical' => true,
'labels' => $labels,
'show_ui' => true,
'show_admin_column' => true,
'query_var' => true,
'rewrite' => array( 'slug' => 'topic' ),
));
}

Reference : https://www.wpblog.com/create-custom-taxonomies-in-wordpress/