[Waiting for user feedback] Intermittent product URLs using default language category slug causing redirect loops when using %pr...

Dear Andrey,

thank you for your clarification.

We understand that, without clear steps to reproduce, this can be difficult to investigate.

However, we believe we have already identified some consistent signals that may help narrow down the issue.

In particular:

- The problem affects product URLs in the secondary language when using %product_cat% in the permalink structure

- The category slug occasionally falls back to the default language, resulting in mixed-language URLs

- This triggers redirect loops, as WPML attempts to resolve the correct URL

- Resetting permalinks and purging Litespeed cache immediately resolves the issue, but only temporarily

This behavior suggests that, at certain moments, the permalink may be generated with an incorrect or incomplete taxonomy translation state.

Additionally, while investigating this, we found similar reports online describing very comparable behavior (mixed-language slugs and redirect loops in multilingual setups), which seem consistent with what we are experiencing.

We understand that there are no officially known conditions for this, but based on both our observations and these similar cases, it appears that under certain circumstances the category slug used in the URL may not match the expected language.

In order to proceed with debugging on our side, it would be very helpful to understand where this logic is handled.

Specifically:

1) At which stage WPML resolves the translated product category when building URLs with %product_cat%

2) Which component (WPML core, WCML, or WordPress itself) is responsible for selecting the taxonomy slug in the final URL

3) If there are any hooks, filters, or internal functions involved in this process that we could monitor

We do have a developer available and are fully willing to investigate further, but without insight into how this part of WPML works internally, it is difficult to proceed effectively.

Given that the issue is intermittent and cannot be reliably reproduced, we would appreciate if this could be escalated for a more in-depth technical review.

Thank you again for your support.

Hello,

our developer has now investigated the issue further and provided additional findings that may help narrow it down.

According to our developer, the class you mentioned seems to be mainly responsible for converting existing links inside saved database content (for example hardcoded links in post_content).

However, our issue appears to happen during dynamic permalink generation, not while processing saved content.

We are seeing it in contexts such as sitemap generation and other runtime permalink generation flows, where product URLs are built dynamically through WordPress/WooCommerce filters.

Because of that, it seems unlikely that absolute-links.class.php is the origin of the issue, although it may still be involved later in the process.

What is your view on this?

To investigate further, we added a debug filter on post_type_link and were able to capture the issue in real time.

Here is an example log entry showing the problem:

```
{
"ts": 1775561645,
"event": "TO BE FIXED",
"post_id": 23689,
"post_slug": "sample-product",
"it_slug": "italian-category-slug",
"en_slug": "english-category-slug",
"wpml_term_id": null,
"original_url": "/en/shop/italian-category-slug/sample-product/",
"fixed_url": "/en/shop/english-category-slug/sample-product/",
"request_uri": "/en/shop/another-category/another-product/?add-to-cart=12345",
"wpml_lang": "en",
"is_admin": false,
"doing_cron": false
}
```

As you can see, the permalink is clearly being generated in an English context (wpml_lang = en, /en/ path), but the category slug inserted into the URL is still the one from the default language.

We are continuing to investigate possible patterns, but this confirms that the glitch is already present at the post_type_link stage.

Do you have any specific technical suggestions based on this log?

We are also attaching the debug code used for this test, in case it helps you understand where the permalink generation flow may be going wrong during initialization.

Any guidance on which WPML/WCML component is responsible for injecting the translated %product_cat% slug at permalink generation time would be very helpful, so we can continue with more targeted tests.

Thank you.

```
<?php

namespace Debug\WPMLSlugIssue;

/**
* Plugin Name: WPML / WCML / WooCommerce - Debug %product_cat%
* Description: Temporary debug helper for multilingual product permalink generation.
*/

define( 'WCML_SLUG_FIX_DEBUG', true );
define( 'WCML_SLUG_FIX_VERBOSE', false );

/**
* Debug Italian category slugs appearing in English product permalinks.
*
* Runs late (priority 99) so it acts as a safety net after WPML/WCML
* have already had their chance to build the URL.
*/
add_filter( 'post_type_link', __NAMESPACE__ . '\debug_wcml_english_category_slug', 99, 4 );
function debug_wcml_english_category_slug(
string $permalink,
\WP_Post $post,
bool $leavename,
bool $sample
): string {

if ( $post->post_type !== 'product' ) {
return $permalink;
}

static $logged_ids = [];
if ( defined( 'WCML_SLUG_FIX_VERBOSE' ) && WCML_SLUG_FIX_VERBOSE ) {
if ( ! isset( $logged_ids[ $post->ID ] ) ) {
$logged_ids[ $post->ID ] = true;
error_log( '[WCML_SLUG_FIX][HEARTBEAT] ' . wp_json_encode( [
'ts' => time(),
'post_id' => $post->ID,
'permalink' => $permalink,
'wpml_lang' => apply_filters( 'wpml_current_language', 'unknown' ),
'is_admin' => is_admin(),
'request_uri' => $_SERVER['REQUEST_URI'] ?? 'CLI/cron',
] ) );
}
}

// Example default-language slugs to watch for.
static $default_language_slugs = [
'default-category-a',
'default-category-b',
'default-category-c',
];

static $slug_cache = [];

$is_english_context = ( strpos( $permalink, '/en/' ) !== false );

if ( ! $is_english_context && function_exists( 'apply_filters' ) ) {
$active_lang = apply_filters( 'wpml_current_language', null );
$is_english_context = ( $active_lang === 'en' );
}

if ( ! $is_english_context ) {
return $permalink;
}

$matched_default_slug = null;

foreach ( $default_language_slugs as $default_slug ) {
if ( strpos( $permalink, '/' . $default_slug . '/' ) !== false ) {
$matched_default_slug = $default_slug;
break;
}
}

if ( $matched_default_slug === null ) {
return $permalink;
}

if ( ! isset( $slug_cache[ $matched_default_slug ] ) ) {
$default_term = get_term_by( 'slug', $matched_default_slug, 'product_cat' );

if ( ! $default_term || is_wp_error( $default_term ) ) {
_wcml_slug_fix_log( 'TERM_NOT_FOUND', $permalink, $post, $matched_default_slug, null );
return $permalink;
}

$translated_term_id = apply_filters(
'wpml_object_id',
$default_term->term_id,
'product_cat',
false,
'en'
);

if ( ! $translated_term_id ) {
_wcml_slug_fix_log( 'EN_TERM_ID_MISSING', $permalink, $post, $matched_default_slug, $default_term->term_id );
return $permalink;
}

$translated_term = get_term( (int) $translated_term_id, 'product_cat' );

if ( ! $translated_term || is_wp_error( $translated_term ) ) {
_wcml_slug_fix_log( 'EN_TERM_INVALID', $permalink, $post, $matched_default_slug, $translated_term_id );
return $permalink;
}

$slug_cache[ $matched_default_slug ] = $translated_term->slug;
}

$en_slug = $slug_cache[ $matched_default_slug ];

if ( $en_slug === $matched_default_slug ) {
_wcml_slug_fix_log( 'SLUGS_IDENTICAL', $permalink, $post, $matched_default_slug, null );
return $permalink;
}

_wcml_slug_fix_log( 'TO BE FIXED', $permalink, $post, $matched_default_slug, null, $en_slug );
return $permalink;
}

function _wcml_slug_fix_log(
string $event,
string $original_url,
\WP_Post $post,
string $default_slug,
?int $wpml_term_id,
?string $en_slug = null,
?string $fixed_url = null
): void {
if ( ! defined( 'WCML_SLUG_FIX_DEBUG' ) || ! WCML_SLUG_FIX_DEBUG ) {
return;
}

$context = [
'ts' => time(),
'event' => $event,
'post_id' => $post->ID,
'post_slug' => $post->post_name,
'it_slug' => $default_slug,
'en_slug' => $en_slug,
'wpml_term_id' => $wpml_term_id,
'original_url' => $original_url,
'fixed_url' => $fixed_url,
'request_uri' => $_SERVER['REQUEST_URI'] ?? 'CLI/cron',
'wpml_lang' => function_exists( 'apply_filters' )
? apply_filters( 'wpml_current_language', 'unknown' )
: 'wpml_unavailable',
'is_admin' => is_admin(),
'doing_cron' => defined( 'DOING_CRON' ) && DOING_CRON,
];

error_log( '[WCML_SLUG_FIX] ' . wp_json_encode( $context ) );
}
```

Hello Andrey,

thank you for your reply.

However, at this stage we need more concrete technical guidance in order to move forward.

In our previous message, our developer raised specific points and questions based on a clear technical analysis. In particular, we explained that the issue occurs during dynamic permalink generation (for example within the post_type_link filter), and not in the processing of saved content.

We also shared a real log example showing the incorrect behavior at that exact stage.

At the moment, we are not receiving any direct feedback on those points, and this makes it difficult for us to continue the investigation.

You mentioned that we are on the right track, but without more specific input we are left without direction.

Could you please review our previous message again and provide a more concrete and responsible answer to the technical questions raised there?

Thank you.

We kindly ask you to allow us a bit more time, and therefore to keep this thread open. The analysis and debugging are currently in progress, and we may well need your assistance again.