We use WP, ACF Pro and WPML pro on our website cms. All plugin versions are up to date. We use Crowdin as Translation management system, where our translation agency receives the translation jobs and sends them back to us.
We set image fields to "CopyOnce" as we want to show localized version of our software depending on the language of the page, but have the original (English) image shown on the FR or Japanese pages until we have the localized images ready.
However we tested the feature and the ACF Image fields are not editable in the target language versions of the pages.
Is there any documentation that you are following?
You can play on our staging website, for instance on the front page: hidden link
-> hidden link
-> hidden link
you will need login credentials that I can give you once this post is set to private.
I join the original language (English) and the French counterparts. As you can see, there is no Edit function on the image in the French translation.
We tried both settings: CopyOnce and Translatable, none had the intended behaviour.