I have registered a custom taxonomy on "post" named "cat_modules" with this args:
'rewrite' => array( 'hierarchical' => true, 'slug' => '/', 'with_front' => false )
'hierarchical' => true to have the url structure like 'category/subcateogry' and I used
'slug' => '/' to remove the "cat_modules" from the slug.
These work well on the archive pages but all posts and pages return a 404 error.
If I remove
'slug' => '/' from the args everything work well.
P.S In this web site is installed WPML.