How can I get a report of the number of words/strings translated per user?

You can watch this video or follow the instruction below.

Go to the Crowdin Khan Academy project settings page in the URL, then click on Reports in the top menu, and custom report in the side menu. From there you can see a form to show various properties such as Total words translated, Total strings translated, etc. on a per language basis. You can also look at a particular date range to know who translated what recently: