It would be much easier to fix your problem with a larger code snippet.

Not a CODE reference at ... line 53, <DATA> line 1. 
if ($q->('lang') eq '' || $q->('lang') eq $bookinfo[1]) {
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This looks like you're dereferencing $q and calling it as a subroutine call. What does $q contain? If it's a hash reference, then to get the 'lang' key out, you should do this instead:

$q->{'lang'}
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Note the curly braces, instead of parentheses.

Alan