You need to add 'use utf8;'

perl -we 'use Unicode::GCString;use Unicode::Normalize;$t="Hütte";prin
+t length("$t");$g=Unicode::GCString->new("$t");print $g->columns'
66
[download]

perl -we 'use utf8;use Unicode::GCString;use Unicode::Normalize;$t="Hü
+tte";print length("$t");$g=Unicode::GCString->new("$t");print $g->col
+umns'
55
[download]

IIRC, the interpreter always uses ISO-8859-1 for the script unless you add 'use utf8;'