You mean a dictionary not a true translation of sentences.

I don't know if there is any free data out there, there are similar services online tho which might have an API:

Search: hindi dictionary - Google Search

This looks like what you want: Shabdanjali - English Hindi Dictionary | www.shabdkosh.com

The coverage of words might small tho.

More: hindi dictionary download gpl - Google Search

__________________
AKA Martin Gallagher