LANG=a_b luatex
produces the error
Unable to read environment locale:exit now.
and any supplied file is ignored
presumably from here in luaint.w
env_locale = setlocale (LC_ALL, "");
if (!env_locale) {
fprintf(stderr,"Unable to read environment locale:exit now.\n");
this came up on stackexchange with a user with locale including
LANG=en_DE.utf8
(German English?)
https://tex.stackexchange.com/questions/374303/luatex-error-unable-to-read-environment-localeexit-now
I'm not sure if luatex could be made to work if LANG is set to an
unknown value (eg just act as if it was C)?? but if not, could the
error message be a bit more informative? "Unable to read" doesn't seem
to suggest "set to wrong value"
David
