Way back in 1992 Udit Narayanji was recording a song for Feroz Khan's movie Yalgaar, the lines of the song went like' Aakhir tumhe aana hai zara der laegi' , Uditji was doing fine in practice session , but whenever recording started he sang: .......jara der lagegi.....
It took some more sessions then it was fine, (Uditji being from land of Bihar).
Those of us who have stayed in & around West Bengal know that many of us can't spell R properly, this is seen in song: 'pardesi pardesi jana nahi'(Raja Hindustani): R in Pardesi is the landing note, despite that Kumar Sanu hasn't said this note properly even in the final recording.
Both of these songs were nominated for National Filmfare Award. And both of these singers went on to become one of the most accomplished Hindi music singers.
Those who have listened to Yesudas in Hindi songs will agree that the simple innocence & emotion of his voice made everyone take notice & hum with him...... (Now he couldn't establish a place in Hindi music was because of the fact: that era belonged to the Golden voice of Mohd Rafi/Kishore da, for that matter no one from any part of India survived in Male Hindi singing as long as they lived).
Keep a hand on your heart and tell me: how many of us have noticed a diction problem when AR Rehman sings; Dil Se or the song which brings us to tears: Ye jo desh hai tera(Swadesh)........not to mention KK, Shankar Mahadevan & others who speak Hindi very well.
Music in itself is a language and doesn't need words to communicate/sweep across..all it needs is a heart ready to accept music.
My humble opinion only........sorry for raking this issue again.