Talking to myself here, but for interested readers, found a solution now for this problem, via functions.php.
For the following code a fieldgroup “Mygroup” is added to two custom post types “aaaa” and “bbbb” via ACF PRO.
The javascript-code then hides that fieldgroup if not “xxxx” or “yyyy” appears in the slug of the posts of these post types.
As WPML with 2 languages is used on the site, the code looks for the normal “acf-mygroup” and also “acf-mygroup-2” for the 2nd language, the fieldgroup has the same title in both languages.
http://pastebin.com/QxyRwst2
