Premise: "Ae Dil Hai Mushkil" (English: "This Heart is Complicated") is a Hindi song from the soundtrack of the Indian film "Ae Dil Hai Mushkil". It is written by Amitabh Bhattacharya, composed by Pritam and sung by Arijit Singh. The music video of the song is picturised on actor Ranbir Kapoor.
Hypothesis:  Amitabh Bhattachary wrote all his songs in Hindi.