Try utf8::all. It's not universal, because it handles only the core functionality, not libraries. Your use case can be much simplified, though. I strongly suspect you have too much code. Consider:

• HTTP::Response provides both content (returns octets) and decoded_content (returns characters, appropriately decoded from Content-Type header).
• decode_json wants to consume octets.

This means the following DWYW:

use LWP::UserAgent qw();
use JSON::MaybeXS qw(decode_json);
my $ua = LWP::UserAgent->new;
my $res = $ua->get('https://ru.wikipedia.org/w/api.php?action=query&fo
+rmat=json&formatversion=2&list=allusers&auactiveusers&aufrom=%D0%91')
+;
die $res->status_line unless $res->is_success;
my $json_OCTETS = $res->content;
my $all_users_CHARACTERS = decode_json $json_OCTETS;
my $continue_aufrom_CHARACTERS = $all_users_CHARACTERS->{continue}{auf
+rom};
[download]

Your CGI script's templating system should take care to produce UTF-8 encoded octets. If you don't have one, then either one of

• use Encode qw(encode);
  my $continue_aufrom_OCTETS = encode('UTF-8', $continue_aufrom_CHARACTE
  +RS, Encode::FB_CROAK);
  STDOUT->print($continue_aufrom_OCTETS);
  [download]

• binmode STDOUT, ':encoding(UTF-8)';
  STDOUT->print($continue_aufrom_CHARACTERS);
  [download]

is appropriate. The first variant is more robust.

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