Yes, you can save your documents to D:, just select a directory on D: in the save file dialog. If you are editing an old file, use 'File > Save As...' instead.

The shortcut keys for switching keyboard input are usually CTRL+Shift or CTRL+Space, maybe you pressed them by accident? If you don't use a certain language, you can disable it. This link is about how to adding a language, it's easier to remove one, just select one and click on Remove button.