User friendliness includes having sensible defaults. English is a sensible default language. So if I wanted a random month in the default language I'd expect to be able to do

my $month = random_month();
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Now if I wanted an abbreviated random month in the default language I'd expect to be able to do

my $month = random_month(-abbrev => 1);
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Language and abbreviation are two distinct concepts, which indicates you need two parameters to handle them cleanly,