Where to find default stopword lists?

I didn't find a pretty version in the docs. But you can always dig through the original code starting here:

https://github.com/apache/lucene-solr/tree/master/lucene/analysis/common/src/resources/org/apache/lucene/analysis

(Note: stop words for some of the languages that don't have an explicit folder are stored under snowball.)

Hope this helps,
Isabel