If that country/code/message/count combination has already been assigned to, you want to increment the value; otherwise you want to initialize the value to one.

If the value does not already exist, using it will automatically initialize it with the value undef, which in numerical contexts counts as zero. Incrementing undef, i.e. incrementing zero, produces one. So you can collapse your eight lines to:

$hash{$country}{$errorcode}{$message}{$count}+=1;
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