use Encode qw( encode );
my $filehandler = encode('UCS-2le', 'C:\\data.wim');

my $wimfile = new Win32::API("wimgapi", "WIMCreateFile", ['S','C','C','C','C','C'], 'N');
my $value = $wimfile->Call($filehandler,WIM_GENERIC_WRITE,WIM_OPEN_EXISTING,WIM_FLAG_VERIFY,WIM_COMPRESS_NONE,WIM_OPENED_EXISTING);