$ perl -wE'
use utf8;
use CGI;
use Devel::Peek;
use Encode;
my $cgi = CGI->new;

my $test = $cgi->param("test");

Dump $test;
my $x = substr($test, 0, 1);
Dump $x;' "test=%C3%A4"
SV = PVMG(0x81a6fe8) at 0x81ada78
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  IV = 0
  NV = 0
  PV = 0x8309588 "\303\244"\0
  CUR = 2
  LEN = 4
SV = PV(0x82a8758) at 0x82aa8c0
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x8193620 "\303"\0
  CUR = 1
  LEN = 4