Spotlight crashes when entering a specific query string
Old answer:

My first solution was simply reindexing all folders by running

sudo mdutil -E /


This did not help. I then renamed the folder in question, reindexed again, named it back and reindexed another time. The problem has now disappeared.

Update:

The bug seems to have been introduced with the update to Safari 12. As discussed in the apple product forums, a workaround is to disable Bookmarks &amp; History in the Spotlight system preferences.