Add language files in civibuild
What build type are you using, Erik?

The translation files are included in drupal-demo but are commented out in drupal-clean.

Uncommenting the line:

 # extract-url --cache-ttl 172800 civicrm=http://download.civicrm.org/civicrm-l10n-core/archives/civicrm-l10n-daily.tar.gz


in app/config/drupal-clean/download.sh in your local buildkit will mean that localisation files are downloaded as part of the download.

You could go a step further and submit a PR that uncommented that line in buildkit, but that is probably for another day.