Note: Emacs binds C-\ to a function that offers to change the
keyboard input method in the multilingual environment. Viper overrides this
binding. However, it is still possible to switch the input method by typing
\ C-\ in the Vi command state and C-z \ C-\ in the Insert state.
Or you can use the MULE menu on the menubar.
In Vi state, switch to Emacs state; in Emacs state, switch to Vi state.