Well, I'm sure there's an elegant way to do it with the Module, which you should look into and definitely use, but if you just want to get the language value in a $lang variable, there's a lot of ways to do that:

open R, "file" or die "could not open file\n";

while (<R>) {
        my @lines = split (/\n/);
        foreach my $line (@lines){
                next if $line !~ /xml:lang/xg;
                my ($junk, $lang) = split /=/, $line;
                $lang =~ s/^"(.*)">$/$1/;
                print "$lang \n";
        }
}
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It's not the best way to solve the problem, and it's definitely not the shortest way to write it, but it works and makes sense (to me anyway)