I use Arabic and English on daily basis,for switching layouts I use qxkb app which is really effecient and easy to use . some times i need to type special characters ( گ چ ڤ ) etc, and to my suprise this option was already there in qxkb , here is a little illustrative
if there is a poroblem with the graphical user interface , you can copy and paste this command in your terminal
setxkbmap -option -option grp:lalt_lshift_toggle,lv3:caps_switch
,press and hold caps and type the special character, that is =) .