Polylang Pro Slugs Sync Acf

Polylang Pro Slugs, Sync, and ACF

Use this skill when compatibility depends on Pro-only behavior rather than the core Polylang API.

Polylang Pro 3.8.5 adds major behavior in three areas:

• translated and shared slugs;
• duplicate/sync workflows;
• ACF Pro integration.

Guard Pro-only code:

if ( ! defined( 'POLYLANG_PRO' ) ) {
    return;
}

Translated rewrite slugs

Polylang Pro translates rewrite slugs through strings translation. The model scans registered post types, archives, taxonomies, post formats, and miscellaneous bases such as author, search, attachment, page, and the front base.

It stores the computed map in the transient pll_translated_slugs and refreshes rewrite rules after string translations are saved.

Add your plugin's custom slug source with:

add_filter(
    'pll_translated_slugs',
    static function ( array $slugs, PLL_Language $language, PLL_MO $mo ): array {
        $source = 'courses';

        $slugs['myplugin_courses']['slug'] = $source;
        $translated = $mo->translate( $source );
        $slugs['myplugin_courses']['translations'][ $language->slug ] = $translated ?: $source;

        return $slugs;
    },
    10,
    3
);

Rules:

• Register CPTs and taxonomies before wp_loaded; Pro initializes translated slugs on wp_loaded priority 1.
• Flush rewrite rules when your base slug changes, not on every request.
• Do not read get_option( 'rewrite_rules' ) and mutate rules manually. Hook Polylang's slug filters and let the model rebuild.
• Expect object caches: Pro deletes the transient option row explicitly when an external object cache is active.

Shared slugs

Polylang Pro can allow translated posts or terms to share the same slug in different languages. It filters slug uniqueness and query resolution by language.

Compatibility rule: never assume post_name or term slug is globally unique.

Bad:

$post = get_page_by_path( $slug, \OBJECT, 'page' );

Safer:

$post_id = pll_get_post( $source_post_id, $target_lang );

If you must query by slug, include language in the query:

$query = new WP_Query( array(
    'name'      => sanitize_title( $slug ),
    'post_type' => 'book',
    'lang'      => $target_lang,
) );

Pro's shared post slug class adds joins and where clauses for name and pagename queries. Custom SQL must do the same through Polylang's model or avoid slug lookup entirely.

Duplicate and sync workflows

Polylang Pro's sync model can copy or synchronize posts. It sets language early, saves translation groups, copies taxonomies and metas through Polylang sync services, and fires hooks:

• pll_created_sync_post
• pll_save_post
• pll_post_synchronized
• pll_sync_post_fields
• pll_copy_taxonomies
• pll_copy_post_metas
• pll_translate_post_meta

Use hooks instead of re-copying all data after the fact.

Example: exclude volatile meta from sync:

add_filter(
    'pll_copy_post_metas',
    static function ( array $keys, bool $sync, int $from, int $to, string $lang ): array {
        if ( 'book' !== get_post_type( $from ) ) {
            return $keys;
        }

        return array_diff( $keys, array( '_myplugin_render_cache', '_myplugin_last_webhook_id' ) );
    },
    10,
    5
);

Example: translate stored IDs while copying:

add_filter(
    'pll_translate_post_meta',
    static function ( $value, string $key, string $lang, int $from, int $to ) {
        if ( '_myplugin_related_book' !== $key || ! is_numeric( $value ) ) {
            return $value;
        }

        $translated = pll_get_post( (int) $value, $lang );
        return $translated ?: $value;
    },
    10,
    5
);

Do not call private Pro internals unless no public/hook-based integration exists. If you must interact with PLL()->sync_post_model, wrap it in defined( 'POLYLANG_PRO' ), isset(), and method checks because it is not a public stable API.

ACF Pro integration

Polylang Pro's ACF integration requires ACF 6.0+. It is bootstrapped under WP_Syntex\Polylang_Pro\Integrations\ACF.

Important 3.7+ model:

• ACF field groups are not translated anymore.
• Field groups can be displayed by language using a custom ACF location rule.
• ACF labels are translated through strings translation.
• ACF custom field values are handled by Pro's strategy system, not by raw post_meta sync.

Polylang Pro adds a field setting named translations with these choices:

Text-like fields get translate and translate_once; other fields typically get copy/sync choices.

ACF relationship IDs

ACF fields often store post IDs, term IDs, media IDs, or nested arrays containing them. Pro's Dispatcher registers collectors and translators:

• pll_collect_post_ids
• pll_collect_term_ids
• pll_translate_blocks_with_context
• pll_filter_translated_post
• acf/fields/relationship/query
• acf/fields/post_object/query

If your custom ACF field type stores IDs in a custom shape, integrate with these collectors so Pro can export/import and sync them.

Pattern for a custom stored post ID:

add_filter( 'pll_translate_post_meta', static function ( $value, $key, $lang ) {
    if ( '_myplugin_acf_extra_post' !== $key || ! is_numeric( $value ) ) {
        return $value;
    }

    return pll_get_post( (int) $value, $lang ) ?: $value;
}, 10, 3 );

For fields owned by ACF itself, do not duplicate ACF's own meta keys manually. Pro removes ACF metas from generic Polylang sync so its ACF strategy layer can handle them.

ACF labels

ACF field-group, field, custom post type, and taxonomy labels can be translated. The feature can be disabled:

add_filter( 'pll_enable_acf_labels_translation', '__return_false' );

Use this only when another system fully owns ACF label translation. Otherwise leave it enabled and keep labels as stable source strings.

You can extend the field label keys that Polylang translates:

add_filter( 'pll_acf_field_labels_to_translate', static function ( array $labels ): array {
    $labels['my_custom_field_type'][] = 'button_label';
    return $labels;
} );

Common mistakes

• Assuming ACF field groups are translated posts in Pro 3.7+. They are not.
• Copying raw ACF meta after Pro has already applied ACF strategies.
• Looking up translated content by slug without a language filter when shared slugs are enabled.
• Returning translated rewrite slugs after wp_loaded and wondering why rewrite rules do not change.
• Flushing rewrite rules on every request after changing translatable slugs.
• Synchronizing cache/transient/meta fields that should be language-specific.

Cross-references

• Use polylang-object-translations for post/term language assignment and translation groups.
• Use polylang-rest-headless for Pro REST duplication and untranslated-post endpoints.
• Use polylang-wc-compatibility before applying generic Pro sync rules to products or orders.

Verification

Local source checked against:

• Translated slug model: wp-content/plugins/polylang-pro/src/modules/translate-slugs/translate-slugs-model.php
• Shared slug query filters: src/modules/share-slug/share-post-slug.php
• Pro sync model and hooks: src/modules/sync-post/sync-post-model.php
• ACF integration README, field settings, dispatcher, and label filters: src/integrations/ACF/*

References

• Official documentation: https://polylang.pro/doc/developpers-how-to/
• Official documentation: https://polylang.pro/doc/strings-translation/
• Verified source paths:
  • wp-content/plugins/polylang-pro/src/pro.php
  • wp-content/plugins/polylang-pro/src/modules/translate-slugs/translate-slugs-model.php
  • wp-content/plugins/polylang-pro/src/modules/share-slug/share-post-slug.php
  • wp-content/plugins/polylang-pro/src/modules/share-slug/share-term-slug.php
  • wp-content/plugins/polylang-pro/src/modules/sync-post/sync-post-model.php
  • wp-content/plugins/polylang-pro/src/modules/sync-post/sync-post.php
  • wp-content/plugins/polylang-pro/src/integrations/ACF/README.md
  • wp-content/plugins/polylang-pro/src/integrations/ACF/Main.php
  • wp-content/plugins/polylang-pro/src/integrations/ACF/Field_Settings.php
  • wp-content/plugins/polylang-pro/src/integrations/ACF/Dispatcher.php
  • wp-content/plugins/polylang-pro/src/integrations/ACF/Labels/Field_Groups.php