This thread is resolved. Here is a description of the problem and solution.
Problem:
If I use get_post_meta WordPress function to get the ACF Clone field, the result is the original language ID on a translated page which is wrong. For example:
I created a WordPress, WPML, ACF Pro and Multilingual installation that you can access here:
hidden link
Please replicate the issue about the copied gallery items with prefix option and add your code to theme's functions.php file or somewhere else (inform us) to see ethe result and the inconsistency.
In each page there are two var_dump(): the first is from a normal gallery (ids are translated), the second is from a cloned + prefix gallery (ids are not translated)
I am going to report this to the second-tier support for further investigation.
Just to be on the same page, as already get_field function retrieves the correct ID for the Clone Gallery, there is a way to achieve this and it will get a lower priority for the get_post_meta method.