Can't set right alt + shift to switch language repeatedly

I successfully managed to get alt + shift to swich languages. However when I use the left alt + shift key combination to switch languages I can do it repeatedly to go back and forth between languages, but this is not the case with the right side of the keyboard.
How can I get right alt + shift to behave the same as the left side combination?
Thanks in advance.

The problem occurs because "Right Alt" is used as "3rd level chooser key", to solve this problem :

• open Tweaks (you can get it from Ubuntu Software Center)
• select "Keyboard & Mouse"
• select "Additional Layout Options"
• select "Key to choose the 3rd Level"
• choose "Right Alt never chooses 3rd level"

you can assign another key as 3rd level chooser if you still need to access those keys