A few (ok, ten) years ago, I needed to generically pluralize English words in ColdFusion. Also, I wanted to be able to reverse that out ("singularize" as it were). This should be a really easy problem: If it ends with an "s" then add "es"; If it ends with a "y" then ditch the "y"; Otherwise just add "s". It turns out, though, that English is delightfully complicated.
I created it ten years ago, and I've used a fair number of times since. It isn't complicated enough that I've needed to update it much in that time.