I was just playing around with the new language command, but I couldn't get the list to work on a WP 4.7.9 install: <img width="763" alt="image 2018-01-25 at 8 18 39 am" src="https://user-images.githubusercontent.com/83631/35375860-db2bf97a-01a8-11e8-8f44-c76de95f6aa6.png"> I had the same problem with themes as well.