Overview of the issue
If your product attributes use the same slug between languages and you update it later, the translated products that use this attribute for variations will lose the connection (the attribute will be changed to Any).
- Go to WooCommerce → WooCommerce Multilingual → Attributes and translate the terms.
- Edit the product (in the default language) and scroll to Product Data → Variations. You will see that the variation is missing the attribute (it will be set to Any).
- Select the attribute again and save.
- Update the translation.
Now it will work correctly even if you decide to modify the translated slug again.