I have finally been able to make some progress towards translating Hudson in French. The latest version (1.181) will now display automatically in French if your web browser is appropriately configured.
I have translated all properties files, which is pretty good (there much be a hundred of them),but I still need to work on the HTML pages, which are used to provide online help. This will take probably much longer.
The frustrating thing is that a lot of the text is still hard-coded in Jelly files or in even in Java. I guess my next step will be to work on the code itself.
Let me know if you want to help!