For this one (Left Alt + Shift) to change languages sometime also can not use, Because different setting some computer use (`) , (Left Alt + Shift), Ctrl + Shift) . So we have to use shortcuts according to setting as be low:
Control panel ==> Region & Languages==> Keyboard & languages ==> Change keyboard ==> Advanced key setting==>Change key sequence ==>then click on the bottom as you want it to be your shortcut ==> ok (For Win 7)
Best Regards
Nilatsa