Since the structure is one level deeper than you thought, you need to add another loop. Try this:

            my @categories = $decoded_json[0];
            foreach my $category (@categories){
                foreach my $record (@$category) {
                    print Dumper $record;
                    print "Translation for $record->[0] is $record->[1
+]\n";
               }
           }
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Hope this helps!