[Resolved] Problem Description (English)

Problem:
You have a custom taxonomy called 'fitment' assigned to WooCommerce products, set as Not Translatable in WPML. Terms are created in Polish and work correctly in Polish products, but in the English product edit screen, the taxonomy is visible without any terms to select. You want the same taxonomy terms to be shared across all languages without needing translations.

Solution:
The issue might be related to the

meta_box_cb => 'post_categories_meta_box'

in your custom code. This meta box forces WordPress to render the classic Categories-style checklist metabox for this taxonomy, which relies on wp_terms_checklist() → get_terms(), and WPML filters get_terms() in wp-admin to the current admin language. If your Fitment terms are created only in the default language and don’t have term translations, the checklist in the secondary language can appear empty. To resolve this:
1. Remove the

meta_box_cb => 'post_categories_meta_box'

from your custom code to test if the terms show in the translation without it.
2. Register the taxonomy on init with priority 0 to avoid issues with it being registered too late.

If these steps do not resolve the issue, or if the solution becomes outdated, we highly recommend checking related known issues at https://wpml.org/known-issues/, verifying the version of the permanent fix, and confirming that you have installed the latest versions of themes and plugins. If the problem persists, please open a new support ticket.