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(
  ZM => [ [20470, "20470:ZM:Samfya:Africa"],
...
  ZW => [ ... ],
  ...
)

use warnings;       # just for debugging
use strict;         # just for debugging
...
for $k (sort keys %h) {
  print $_->[1] for splice [sort {$b->[0]<=>$a->[0]} @{$h{$k}}], 0, 4
}                   # -n