Kalanyr: I do not have the file at that stage (this check is performed at update, there is also an MD5 check in verify when you do have the file but I'm having difficulty thinking of a context where calculating the MD5 in place of an authoritative one would be useful there )
Ooops, a bit of omission in my thinking - you can't calculate an MD5 if you don't have the file and you need to download it :) It would be useful to clean the directory of duplicates, but will also result in re-download (and deletion) every time... That's a bad solution, I agree.
But, as it is the only game (two IDs actually) that has this issue, I would think of hard-coded workaround, i.e. if extras are being downloaded for one of these two IDs, skip downloading these few files if non-English version(s) is selected. However, this solution is ugly enough I would understand if you decide to not implement it at all, I'd rather waste 65 GB of my disk space than have the script code messed up.
Thanks for looking into it, whatever you decide :)
EDIT: Maybe I will just use:
-skipfiles *witcher*(1)*
It would do the work, at least for my collection - luckily, it seems GOG is not using this in any file names, so even "*(1)*" mask should do.
EDIT2: Yep, that did the trick.