Idea: Farsi and Russian both have simple list of vowel sounds and no diphtongs. Making it hard/obvious when attempting to speak english, which is rife with them and many different vowel sounds
While Persian has only two diphtongs and 6-8 vowels, Other Languages of Iran are full of them(e.g. Southern Kurdish speakers can pronounce 12+1 vowels and 11 diphtongs). I find it funny if all Iranians are speaking English with the Persian accent.