There are whole libraries devoted to the intricacies and irregularities of the English language. When Glassboy talks about 'source language' you might take a half-hour or so to consider how many source languages there are for English, starting with all the linguistic groups that invaded the British Isles, followed by all the linguistic groups that got invaded by the British, adding in the partner/rival countries such as the Dutch, Spanish and Portuguese, and then considering all the franchise countries that work their own magic - the Kiwis, Australians, Americans, Canadians, South Africans etc. The wonder is that any of the native speakers manage English, let alone how so many 'second-language' speakers can speak and write it so well.
But, as Simon and Glassboy suggest, there would have to be a monumental set of rules, exceptions and alternatives defined to get a computer application to decipher it all.