Detect when running on a system without locales installed

[mwvaughn]

Some (Ubuntu, we're looking at you) systems don't set a reasonable locale and in fact default to ANSI_X3.4-1968, a fancy version of ascii. This is annoying since we can't actually resolve this deficiency by installing Python dependencies, as the C locales are missing entirely. This surfaces most often when people are containerizing a Python application.

A suggested solution is to just check python3 -c 'import sys; print(sys.stdout.encoding)' and see if it returns utf-8, failing with a helpful note about how to install locales.