At first just create regular field, for example product field:
I've also added pricing and character limit to make this more interesting.
Hit "Submit" to save your changes.
Then right below the fields we were editing you can see this box:
The checkbox makes all "Product Fields" fields type translatable. Then you can select what to do with custom taxonomies - just "do nothing".
And below is even more - current field's settings:
I've selected to just copy 'pricing_value', 'pricing_method' and 'character_limit', as those doesn't need any translation.
Now at the right sidebar find this box:
This sets the current language of currently edited field. You can click on "+" to add translation in another language.
After reloading of page you'll see the same content mostly (or completely the same - if you also checked "duplicate"), but right box will be different:
From now you can switch between versions by clicking "pencil" icon. Note that those are actually two different custom fields that was created - they have different wordpress post id and may have different unique field (if you don't duplicate the field). So because of that one of the fields may be "enabled" while other may be "disabled" - this will result in working field in one language, and missing - in another. In some cases it may be desired behavior, in some - not.