Problem:
Inside the Plugin for WooCommerce Product-Add-Ons, the fields are not appearing on the WPML Advanced Translation editor, if you use numeric field values.
Solution:
The Advanced Translation Editor by default does not translate fields that include numeric values only, as it is designed to only translate text and usually does copy numeric value fields automatically.
In order to be able to translate numeric values with the Advanced Translation Editor please add this constant inside the functions.php file of a Child Theme: