Convert from Modern English to Old English. Old English is the language of the Anglo-Saxons (up to about 1150), a highly inflected language with a largely Germanic vocabulary, very different from modern English. As this is a really old language you may not find all modern words in there. Also a single modern word may map to many Old English words. So you may get different results for the same sentences different time.
If you like our Old English why not create a great app with it by using our Old English API?