I think CPAN is good enough for all this.
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Tree::Nary is propably not the best module, but if you remove that _that_ might force to rewrite or reinvent what Tree::Nary does already.
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If you have a better idea of the same module ask the author and maintain the module.
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If your module is very different, since your interface change, release a new module. And describe the need for the new module in your pod.
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If Lingua::NL::Numbers generates wrong output use http://rt.cpan.org/ to inform the author and others about the bug.
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And for Lingua::IT::Numbers I recommend provide a patch to the author and put the patch and a discription on http://rt.cpan.org/.