System language, can I change it after installation? I have Craft on local (Pro edition) that was installed with French as the system language.  Is there a way to change to another language (English for example) for the control panel? I want to change the system language, not the content of my entries (localisation).
If you go to Settings->Locales in the control panel, you can add "English - en" as a new locale/language to Craft.

From there, you can can what language the Control Panel will display on a per user basis by going to the user's account and setting the "Preferring Language" setting.

As J. Baptiste pointed out, you can also set what the default Control Panel language should be for all users by setting the defaultCpLanguage config setting.