Apertium is a rule-based machine translation platform. It is free software and released under the terms of the GNU General Public License.
Languages supported in stable version: Asturian, Basque, Breton, Bulgarian, Catalan, Danish, English, Esperanto, French, Galician, Icelandic, Macedonian, Norwegian (Bokmål and Nynorsk), Occitan, Portuguese, Romanian, Spanish, Swedish and Welsh; many more are under development. More Info »
In addition to translating through the web page, you can download and run the translator on your own machine, both on Windows, Mac and GNU/Linux systems.
Source code : https://sourceforge.net/projects/apertium/files/