It's a reference to an array of hash refs, so you must de-reference it first.

#!/usr/bin/perl
use strict;
use warnings;

my $VAR1 = [
          {
            'sourceL' => 'spacecraft',
            'source' => 'MT',
            'targetL' => 'vaisseau spatial'
          }
        ];

for (@$VAR1) {
    print ucfirst $_->{targetL} ;
}
[download]

See perldsc for lots more.