You need to use "Menu Item Associations" section of menu item configuration. It clearly says:
This choice will only display if the Language Filter parameter 'Menu Associations' is set to 'Yes'. Choose a menu item for the target language. This association will let the Language Switcher module redirect to the associated menu item in another language. If used, make sure to display the Language switcher module on the concerned pages. A menu item set to language 'All' can't be associated.