The oldest snapshot on https://languagetool.org/download/snapshots/ is from 2018-06-08. How do I get a snapshot from before this date?
Old snapshots get deleted after some time. To get an old version, you need to get it from git and build it yourself. Use a command like this to get the old source from a given date:
git checkout `git rev-list -n 1 --before="2017-10-06 13:37" master`
mvn clean package and
git checkout master to get back to the current state.