As always, the devil is in the detail...
On Mac OS X v10.7.5 (Lion), to fix some Django error, in my ~/.bash_profile
I've set:
export LANG=en_EN.UTF-8
export LC_COLLATE=$LANG
export LC_CTYPE=$LANG
export LC_MESSAGES=$LANG
export LC_MONETARY=$LANG
export LC_NUMERIC=$LANG
export LC_TIME=$LANG
export LC_ALL=$LANG
And in turn for a long time I got that warning when using Perl.
My bad! As I've realized much later, my system is en_US.UTF-8
!
I fixed it simply by changing from
export LANG=en_EN.UTF-8
to
export LANG=en_US.UTF-8