On install/remove of locales-XX, 2 scripts are called (locale_install.sh & locale_uninstall.sh) that copy encoding definitions in /etc. This is no more needed since UsrMove. This was needed in the old days when we run some things before mounting /usr but now /usr is mounted very early in initrd before running systemd so that's now useless and just eat disk space and do useless I/O at (un)install time...