Slightly going Off-Topic:

May I point your focus on my code comments in my first response:

Should I move

while( my $q = new CGI::Fast ){
        $q->header(-charset => 'utf-8'); # as I now set :utf8 in cgiap
+p
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the modification of the $q->header to charset utf-8 into CGI::Application's App.pm cgiapp_prerun() stage? Currently I only have it at this very early app.cgi position as I am unclear about when CGI::Application creates the CGI.pm / CGI::Fast object and I am unsure if on-init of this object the charset declaration is taken into account...