This isn't slick, but it is straight-forward and seems like it should be fairly fast:

my @result= do {
    my %temp;
    @temp{@employee}= ();
    grep ! exists $temp{$_}, keys %languages;
}
[download]

Then again, with Perl and an N of 6, I don't think O(N*N) is much of a problem. ;)

        - tye (but my friends call me "Tye")