Define a hash table with the translation that you desire. This will be compiled - it only happens once. Then just access that hash table to print the text that you desire.

#!/usr/bin/perl -w
use strict;

my %xlateNum2Text =  qw (0   January
                         1   Febuary
                         2   March
                         3   April
                         4   May
                         5   June
                         6   July
                         7   August
                         8   September
                         9   October
                         10  November
                         11  December                  
                       );

my($day, $month, $year)=(localtime)[3,4,5]; 
        $year = $year + 1900;
print "day=$day, month=$month, year=$year\n";  

print "day=$day, month=$xlateNum2Text{$month}, year=$year\n";

__END__
Prints:
day=30, month=7, year=2012
day=30, month=August, year=2012
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Update:
Yes, it is possible to use an array instead of a hash table. However, I would recommend making the intent and translation very clear by using a hash table. In the code above, it is clear what number corresponds to what text, ie, that January is zero, not one.