How to Change Language of your iPhone 6s plus and its Menus

follow these steps:

1. From your Home Screen, go to Settings.
2. Choose 'General' from the drop-down menu.
3. Select 'Languages & Region' from the drop-down menu.
4. Select 'iPhone Languages' from the drop-down menu.
5. Type the language you'd want to add into the Search Bar.
6. Click 'Change to [Language]' to confirm your choice.