Here's a Python script for pluralizing English nouns with 99% accuracy:
samePlural = (lambda word: word in ('sheep', 'deer', 'fish',
'moose', 'aircraft', 'series', 'haiku', 'scissors'),
lambda word: word)
alwaysAddS = (lambda word: word in ('delf', 'pelf', 'human',
'roman', 'lowlife'),