I was running into a frustrating issue when trying to download a bunch of nltk test corpora in Python Launcher: the launcher kept saying it could verify my SSL certificate, which meant that I was unable to download the materials I wanted.
It turns out that the way around this problem is as follows:
1. Create an unverified SSL context
>>> import ssl >>> ssl._create_default_https_context = ssl._create_unverified_context
2. Then run the download
>>> import nltk >>> nltk.download()
3. Download the packages in Launcher