[Escalated to WPML Developers team] wcml_register_endpoints_query_vars registration switches locale

I believe in WCML_Endpoints the method should be this

	public function get_endpoint_translation( $key, $endpoint, $language = null ) {
		return apply_filters( 'wpml_get_endpoint_translation', $key, $endpoint, $language );
	}

Instead of this

	public function get_endpoint_translation( $endpoint, $language = null ) {
		return apply_filters( 'wpml_get_endpoint_translation', $endpoint, $endpoint, $language );
	}

I am (and other extensions are using it like this)

The issue lies in WCML (maybe a rewrite at some point) because as I already explained

$obj is an instance of WCML_Endpoints but it's signature does not match that of the example, it takes 2 arguments $endpoint and $language while another similar class takes $key, $endpoint and $language

That means that with the example provided, the $language parameter is set to 'view-subscription' which is obviously not a valid language code and was meant to be $key and $endpoint.
That means that it will lookup the string translation of the endpoint in the language 'view-subscription', which obviously doesn't exists (and spends a lot of time doing so as well by trying to load MO files to init the locale)

As such, the method `WCML_Endpoints::get_endpoint_translation` should be rewritten to this

public function get_endpoint_translation( $key, $endpoint = null, $language = null ) {
    return apply_filters( 'wpml_get_endpoint_translation', $key, $endpoint ?? $key, $language );
}

It appears that I broke the sandbox and I cannot access it to fix the php file, it also had outdated WPML plugin (though this is not an issue to demonstrate the bug)

You can just add the following code in a theme or plugin

add_filter('wcml_register_endpoints_query_vars', 'register_endpoint', 10, 3);

function register_endpoint($query_vars, $wc_vars, $obj)
{
    // Add the translation for the custom "view-subscription" endpoint.
    $query_vars['view-subscription'] = $obj->get_endpoint_translation('view-subscription', isset($wc_vars['view-subscription']) ? $wc_vars['view-subscription'] : 'view-subscription');

    return $query_vars;
}

add_filter('pre_load_textdomain', function ($null, $domain, $mofile, $locale) {
    if ($locale === "view-subscription" && !isset($_GET['bypass'])) {
        echo "The 'view-subscription' locale is being loaded";
        die;
    }
    return $null;
}, 10, 4);

If you load any page you will see that the "view-subscription" locale is being loaded

Look, I am not here looking for feedback on a minimal reproduction.

This is a piece of code that demonstrates that YOUR example is doing something wrong. Which is using an endpoint name as a locale parameter, which obviously doesn't exist and tries to load "view-subscription" as a locale. You said it yourself, locale should be something like "en_US" or "fr_FR" not "view-subscription", so if the die does happen then there is a problem in WPML

What is not correct is either YOUR example or the WCML_Endpoints class. But this example is now widely used in other plugins. So the WCML_Endpoints class needs to be fixed.

If you don't want to implement the fix I provided which is a 2 line patch and improves the performance and reliability of WCML without breaking changes, be my guest.

Again my hook is just a DEMONSTRATION THAT WPML IS SWITCHING THE LOCALE TO 'view-subscription', it was just condensed into something that shows the issue and real usage differs, what is so hard to understand? I did not "invent" the locale parameter

https://developer.wordpress.org/reference/hooks/pre_load_textdomain/

Stop lecturing me about bad usage here. And actually try to understand the issue I'm reporting and if you can't then escalate the example I provided and the suggested patch to developers because they will understand.