Language configuration

Haroopad loads the default language from system automatically. But I think better provide a way of choosing language for user. For myself, I want to use English menus for better communication with my foreign colleagues, but I would keep Chinese as my default OS language...

I don't remember if I could choose language when I installed Haroopad on Windows, but on MacOSX I can't. Anyway, it's not a big issue. Just a small suggestion :)