this is current profile: https://lab.nexedi.com/Kreisel/slapos/blob/master/component/nltk/buildout.cfg
And this is how others use the nltk downloader with buildout: https://github.com/davidjb/mist/blob/master/buildout.cfg#L29
About direct download versus using nltk downloader: According to sebastian, nltk downloader does more than just downloading, it also does some configuration after download (but I did not check the code, so I am not sure),
The sr must have a configuration option for sure to decide what packages to download, because a software using nltk will depend on the availabilty certain packages.
The question which Sebastian and I have is: What is preffered ? A) Using (configurable) direct download or B) using (configurable) download through calling nltk-download ?
B) seems easier to implement (see link above). But we were not sure if it is against SlapOS design to use a downloader script