I've worked on FreeSpeak a couple of years ago, a Python/GTK+/GNOME project to translate text and web pages by querying already existing online translation tools.
PRO: It has been packed for Ubuntu and it has been publicized by a journal in Italy.
CONS: It has been discontinued until now. In fact I restarted the project and I'm doing a huge refactoring because of the ugly code I wrote in the past.
It's already working, but some features are still missing.
The new approach will allow applications to use FreeSpeak as a Python library to embed the translation widgets.
Contact me if you intend to help the project with suggestions, bug reports, critiques and coding.