Unfortunately phpDiplomacy doesn't yet have built-in translation support; so the easiest way to translate phpDiplomacy is to download the source from here, and replace all the English text with translated text.
After doing this your new version of phpDiplomacy will provide a great web-Diplomacy experience in the language you translated to; you can use your code to start up a new phpDiplomacy site for speakers of your language, or send the code to me at kestas.j.k@gmail.com and I will host it for you!
Alternatively, if you're up for a challenge and know some PHP you can help code built-in translation support; this will
allow English speakers to view a site in English, while at the same time allowing French speakers to view the same server
in French. However despite there being some code in place to make built-in translations possible this would be quite a
lot of work to do well!
But if you're not deterred by that, and want to bring your favorite phpDiplomacy community to more people, you can get
the code and the help you need here.
If you have questions or need help feel free to contact other developers in the developer forums, or contact me personally at kestas.j.k@gmail.com