module String::Inflections

def self.plural(rule, replacement)

plural(/(x|ch|ss|sh)$/i, '\1es')
Example:

The replacement should always be a string that may include references to the matched data from the rule.
Specifies a new pluralization rule and its replacement. The rule can either be a string or a regular expression. 
def self.plural(rule, replacement)
  @plurals.insert(0, [rule, replacement])
end