I coded this in half an hour in pure JavaScript preceded by two hours of picking characters out of rare-earth alphabets listed in Wikipedia articles By hand
http://chebmaster.com/rubbish.html
The most hilarious part, most of the substitutes signify more or less the same character in their alphabet.
Sample:
This page performs all processing in your browser. It doesn't send anything anywhere. Id does not depend on a server. You can save it on your PC and it will still work.
turns into
Թהიս פэղჱ չეрфոრმს աלლ პרոᛍվსсᛜնג իנ լოუר ბрո᛭סער. ᛁտ דოჷռნ'տ сჷնד эնჲթփиնг աნჸьхჷրե. ᛁդ դոჱռ нოტ дჷпեнד ჵნ ա სվרվჷр. Յու ცან ռэвե ᛜט ոн ыჵур ᛈႺ աნד иტ ჳიלლ сתилל ьჵרქ.
Area of application: say, the character of your fanfic gets stranded in a different world and has some language problems. Or just encounters something suitably alien.