I forgot to run ulsdata2json.php. When I try to do that, I get this error:

eading langdb.yaml...
PHP Fatal error:  Uncaught Error: Call to undefined function curl_init() in /home/jhsoby/GitHub/language-data/src/util/ulsdata2json.php:28
Stack trace:
#0 {main}
  thrown in /home/jhsoby/GitHub/language-data/src/util/ulsdata2json.php on line 28

Not sure if that's a me-only problem or a wider problem.

You are missing php curl module. Check the docs how to install it on your system. We could add ext-curl to require-dev in composer.json.

Thanks! Did that and submitted another commit (please squash when merging).

Adding ext-curl to composer.json sounds like a good idea, yeah.