A title this would be, had I the originality.

In English, there's no good way to autopluralise just by looking at the last letter.

For example, given Dwarf, Calf, Half, Roof, Loaf, you'd maybe think it safe to say "-f" -> "-ves".
Even (because of Knife, Life) "-fe" -> "-ves".

But Woof, Oaf, Proof, Roof..

Canny programmers know that the right way is to store a conversion list: Oaf -> Oafs, Loaf -> Loaves.

But Staff -> ???
Clearly as a stick, Staff -> Stave, or sometimes Staffs.
And as a body of employees, Staff -> Staff.

As always, there is no easy out, and the only way to make it all work is a syntactic understanding of the language.

Which is what makes the spellchecker in Google wave so amazing... if it lives up to the demo.