How to translate fields with WPML
Advanced Product Fields for WooCommerce is fully translatable with WPML
As you already know, the plugin allows you to add option to your products in two ways: via the Edit Product screen or via the menu WooCommerce → Product Fields.
Depending on which one you chose, your translation efforts will be different
Translating field groups
Pre-config
To translate field groups (accessible through the menu WooCommerce → Product Fields) , you need to set them as “translatable” in WPML.
You can do that by going to WPML → Settings and scrolling to the Post Types Translation section. Find “Product Field Groups” and set it as Translatable:

Translating a field group
If you go to WooCommerce → Product Fields and edit one of your field groups, you’ll notice a new “language” section on the right.
First, switch to the correct editor by activating the WordPress Editor setting:

In the next popup, you can lock this setting for all field groups and apply:

Now, enable the “Duplicate” checkbox next to the language you want to translate and click Duplicate:

Next, click the Edit icon to go to the duplicate:

Next, you’ll see a copy of the field group and you can start translating everything into your target language:

Translating fields on the WooCommerce product screen
Translating fields on the “Edit Product” screen happens in mostly the same way as described above.
Go to WPML → Settings and scrolling to the Post Types Translation section. Find “Products” and “Variation”, and set both to translatable:

Make sure to enable the WordPress Editor setting too on the Edit Product screen like described above.