Comment 52 for bug 1357895

Santiago, I'm surprised that you're not aware of it.

There is another way to work as a Alt+Shift or Shift+Alt:

gsettings set org.pantheon.desktop.gala.keybindings switch-input-source "['<Alt>Shift_L', '<Alt>Shift_R', '<Shift>Alt_L', '<Shift>Alt_R']"