Just came across this post, i’m the one who asked the question on the forum, that you were so kind to answer.

I still use this code, it’s very handy. Maybe someone could write this into a module? But perhaps it will not be needed in SS3.

Just found this kinda related info, which is about copying relations when creating translations – the post is here:
http://www.silverstripe.org/general-questions/show/19990

The code (you might want to add this to your post):
Added the following code at the end of the function createTranslation($locale) in Translatable.php

foreach( $originalPage->many_many() as $key => $className ){
$newTranslation->{$key}()->addMany($originalPage->{$key}()->getIdList());
}

Regards,
Thomas – Nobrainer Web