redirect with variable %title%

You cannot use .htaccess to add a category element to the request. It has no way of knowing what the right category is. The issue is when someone requests /producto/producto_name/, WP will treat it like a category request and fail to find anything. You need to intercept such requests through the “request” filter. Verify the request via query that it’s indeed a product and not an actual category. If so, get the correct category term and construct a proper URL for the product. Then call wp_redirect() using the proper URL.

If the request is indeed for a category, return the passed query var array unchanged.