[Solved] WordPress Custom Taxonomy Slug Using Forward Slash

I have custom post type product and want to attach custom taxonomy for that post type named Product Category. By default that custom taxonomy slug is product-category. What I want is to use custom slug product/category. But, unfortunately, WordPress just ignore that slug and return 404.

Debugging
I looked on the $wp_rewrite variable and found that custom taxonomy rewrite comes after custom post type slug. That was caused the problem.

Solution 1, Using Rewrite Plugin

Surprisingly, my own plugin, Rewrite solves this problem.
All you need to do is reorder the rules so that custom taxonomy rewrite rules placed before custom post type rewrite rules.

See figure below.

Solution 2, Using Code Snippet

add_filter('rewrite_rules_array', 'takien_custom_tax_slug_forward_slash',100);

function takien_custom_tax_slug_forward_slash( $rules ) {
	$slug = 'product/category';
	
	$rule = Array();
	$rule = array($slug.'/([^/]+)/?$' => $rules[$slug.'/([^/]+)/?$']) + $rule;
	$rule = array($slug.'/([^/]+)/page/?([0-9]{1,})/?$' => $rules[$slug.'/([^/]+)/page/?([0-9]{1,})/?$']) + $rule;
	$rule = array($slug.'/([^/]+)/(feed|rdf|rss|rss2|atom)/?$' => $rules[$slug.'/([^/]+)/(feed|rdf|rss|rss2|atom)/?$']) + $rule;
	$rule = array($slug.'/([^/]+)/feed/(feed|rdf|rss|rss2|atom)/?$' => $rules[$slug.'/([^/]+)/feed/(feed|rdf|rss|rss2|atom)/?$']) + $rule;
	
	$rules = $rule + $rules;
	return $rules;
}