[Resolved] Does WPML manipulate the post_parent value for posts?

Thank you for the updates, I can see how you described it.

I am working on it and 'll also discuss the matter with the team. Please note that due to almost end of my shift and weekend ahead, I'll be able to get back to you on Monday as earliest.

Have a great weekend.

Thank you for your patience and cooperation. Our team suggest the following workaround:

1. Add this code in theme's functions.php:

	/**
	 * @link wpmlsupp-11453
	 */
	add_filter('wpml_pre_parse_query', function($q){
		if (empty($q->get('wpml_do_not_adjust_name'))) {
			return $q;
		}
		
		$name = $q->get('name');
		unset($q->query['name']);
		unset($q->query_vars['name']);

		add_filter('wpml_post_parse_query', function($q) use ($name){
			$q->set('name', $name);
			return $q;
		});

		return $q;
	});

2. Then in the WP_Query pass wpml_do_not_adjust_name paramter as true e.g:

$args = array(
  'wpml_do_not_adjust_name' => true,
	'post_type'              => $post_types,
	'post_parent'            => 59,
	'name'                   => 'child-page-b',
	'no_found_rows'          => true,  // used to improve performance.
	'update_post_meta_cache' => false, // used to improve performance.
	'update_post_term_cache' => false, // used to improve performance.
);

NOTE: After making these adjustment WPML will stop translating the slug to secondary language. So it won't display the translated post on 2nd language. Since you are passing the static slug in query we assume you need exactly the post that matching the slug and do not want WPML to interfere with this.

Team further noted:

When you have two posts with the same slug in different post types. WPML tries to resolve the post type to translate the slug in query and this results in getting the CPT post first based on our internal logic.

Without WPML both posts are pulled from DB and one with parent post is displayed based on query. When WPML is active, CPT post is getting pulled and it has no parent thus no post is displayed.

The question is why WPML is not pulling both of the posts, this is because we try to translate the post slug in the query and return our best match.

Team has further escalated the case, however, there's no clear ETA for it to be added in a near future release. As the setup is very unlikely to have same slug in two different post types, you can use the above mentioned workaround for the time being.

I've tested this in the sandbox site, feel free to observe and use in your own site as needed.

Unfortunately there's no such place for now, because the matter has been escalated to our dev team. Usually we create an errata if there are so many reports, so everyone can track and trace. But since this is a very rare case, there's nothing like that.

All I can inform you via this ticket if somehow it isn't archived and the solution is out in the meanwhile.

Please check this guide https://wpml.org/documentation/getting-started-guide/translating-page-slugs/ about slug translations. There a couple of related settings.

Of course that works in the same way, all you need to adjust the parent ID to the translated version of the parent page, and, the child slug to the translated version of the child page, for example:

$args = array(
	'wpml_do_not_adjust_name' => true,
	'post_type'              => $post_types,
	'post_parent'            => 61, // ID OF PARENT PAGE (JAPANESE TRANSLATION)
	'name'                   => 'child-page-b-ja', // SLUG OF CHILD PAGE (JAPANESE TRANSLATION)
	'no_found_rows'          => true,  // used to improve performance.
	'update_post_meta_cache' => false, // used to improve performance.
	'update_post_term_cache' => false, // used to improve performance.
);

Notice the 'post_parent' and 'name' attributes and it works fine on hidden link. Reason is the same as mentioned in the "Note" in my previous message with the workaround.

I'll advise to check WPML Hooks (https://wpml.org/documentation/support/wpml-coding-api/wpml-hooks-reference/), so you can perhaps get an idea how to improve the above mentioned (i.e. getting current language, switching language, getting content in a particular language and etc).