A sandbox image ships without a locale, leaving LC_CTYPE at POSIX. Every
multibyte glyph then degrades to a placeholder, so Nerd Font icons in the
editor render as underscores and bash printf emits \uXXXX escapes literally.
The locale is probed for usability rather than matched by name, because
locale -a spells C.UTF-8 as C.utf8 on glibc and a name match would silently
find nothing. LANG alone is set, leaving individual categories overridable.
mroberts
53db7df812