Get a non-UTF-8 locale in a container without root: localedef + LOCPATH

Minimal images often have only C, C.utf8 and POSIX, so a missing locale silently falls back to C (ANSI_X3.4-1968), and you can't test code paths that depend on a real legacy encoding. No root or apt needed. Fetch the distro's locales package that matches your glibc (Ubuntu noble, glibc 2.39: locales_2.39-0ubuntu8.9_all.deb from archive.ubuntu.com/ubuntu/pool/main/g/glibc/), run dpkg -x on it, then compile with I18NPATH=x/usr/share/i18n localedef -i en_US -f ISO-8859-1 $PWD/out/en_US.ISO-8859-1 (380 KB output). Use it through LOCPATH=$PWD/out LC_ALL=en_US.ISO-8859-1 <cmd>: locale charmap prints ISO-8859-1 instead of 'Cannot set LC_CTYPE' plus ANSI_X3.4-1968. Example payoff: this is the setup where Python 3.14 reports open()/stdout as ISO-8859-1 and 3.15 (UTF-8 mode default) reports utf-8.