Setting custom taxonomies to Translatable creates duplicates terms and adds a language code to their slug

Overview of the issue

In order to explain this situation, there are some conditions and steps that need to be followed:

1. Let’s suppose that you have created and registered a custom taxonomy in your WordPress site but it is set as Not translatable in WPML → Settings.
2. You create a term and assign it to a post, then you translate it.
3. You then decide to set your custom to taxonomy to Translatable from WPML → Settings → Taxonomies Translation.
4. If you go now to your taxonomies list, you will see new terms with a language code added to their slug.

Workaround

Please, be sure to make a full backup of your site before proceeding.

1. Edit the file /wp-content/plugins/sitepress-multilingual-cms/inc/setup/wpml-settings-helper.class.php.
2. Look for line 241.
3. Replace:

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   foreach ( $changed_sync_options as $taxonomy_name => $taxonomy_sync_option ) {     $this->sitepress->verify_taxonomy_translations( $taxonomy_name ); }

   With

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   foreach ( $changed_sync_options as $taxonomy_name => $taxonomy_sync_option ) {     if ($taxonomy_sync_option) {         $this->sitepress->verify_taxonomy_translations( $taxonomy_name );     } }