Comment 7 for bug 425202

Fix committed revision 11546.
Tested successfully on Windows XP and Ubuntu 11.04.

I've modified the strategy so that the messages are translated in the python code and not in script.cpp (using stderr to translate variable content is just not possible).
It should now work with almost all the messages. The remaining untranslated strings are mainly due to incompatibility between the their content and gettext in the python files, and will be worked on later.