perl unicode 报Wide character

node2:/django/mysite/news/templates#echo $LANG
en_US.UTF-8

node2:/django/mysite/news/templates#cat a1.pl 
my $a='中国';
print $a."
";
print length($a);
print "
";

node2:/django/mysite/news/templates#perl a1.pl
中国
6

node2:/django/mysite/news/templates#cat a1.pl 
use utf8;
my $a='中国';
print $a."
";
print length($a);
print "
";
node2:/django/mysite/news/templates#perl a1.pl
Wide character in print at a1.pl line 3.
中国
2

unicode 就会报 Wide character