The hash is a pretty good idea. Of course your current method of assigning the hash is 'pseudocode' because the months to the right of the fat comma (=>) aren't quoted. That could easily be solved by saying my %months = qw/01 January 02 March..../;

There's another way to define the hash using a slice. I'm not sure if it's asthetically more or less pleasing than your version, but it's a few less keystrokes.

my %months;
@months{    '01'..'12', 
            '1'..'12', 
        qw/ jan feb mar apr may jun
            jul aug sep oct nov dec
        / } = ( qw/ 
            January February March April May June July
            August September October November December
        /) x 3;
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Cheers!