Is there a (free) English – Tamil translation software for download / online?
The answer is YES. Visit Google Translate for translating Tamil to and from many languages. This is an alpha version so you may not get the best result always.
There are some long running machine based translation research projects at Universities. But none have given usable product yet. Google is the first to offer translation services for tamil. They also give a translation toolkit that can be used for any language. Wikibhasha is another translation toolkit for Wikipedia developed by Microsoft. Right now thier efficiency for Tamil translation is very rudimentary. It is supposed to get better when more users use it.
Google says that it can bring better automatic machine based translation for Tamil too, if it can get millions of pages of documents with English and Tamil translation side by side. One place where such translated documents may reside with the legal department of the country. It’s in the Government’s hands to give them for public research if not to a private company like Google.