You already have references. So why not pass them?

process_article(*WFH, $locations{$article}, $lists{$list});

sub process_article {
  local(*FH)= shift;
  my($loc, $key)= @_;
  # then use print FH "anything" to print to your file
  # $loc->{keyword} instead of $location{keyword}
  # and $key->[index] instead of $keyword[index]
}
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