How do I get gcc to print localized error messages? (WSL - Ubuntu 16.04)

I figure I'm just missing one step, but no matter what I try, I can't get localized error messages from gcc. And most searches I've tried turn up people trying to disable the messages and use English.

• I've run sudo apt install language-pack-es-base.
• I've run sudo apt install gcc-5-locales.
• I've checked that $LANG = es_ES.UTF-8.
  • and I set LC_ALL, LC_MESSAGES, and LC_CTYPE to the same based on gcc's documentation here, but nothing changed.

apt and other shell commands are printing Spanish messages, why won't gcc? (I'm using gcc-5)