unset LC_ALL LC_NUMERIC
export LANG=de_DE.UTF-8
printf '%.4f\n' 1

LANG=C printf '%.4f\n' 1
LANG=C /usr/bin/printf '%.4f\n' 1

env LANG=C printf '%.4f\n' 1
(LANG=C; printf '%.4f\n' 1)

printf '%.4f\n' 1