Dear Harry Spier,
You have asked for studies/articles, which in my view would be secondary sources. Nevertheless, I’m giving you a good primary source to contact. I hope it will be of some help.
South Indian Carnatic/Classical Music is loaded with songs/hymns depicting a mixture of Sanskrit and different regional languages such as Telugu, Kannada, Malayalam, Tamil. [One main reason for the ‘Tamil nationalists’ to boycott them! ;-) ]
A wonderful musician, Prince Rama Varma (from the erstwhile Travancore Kingdom; a direct descendant of a ruling king and a great composer Maharaja Swathi Thirunal & the famous painter Raja Ravi Varma), considers such songs display a 'maṇipravāḷa style,’ meaning that such songs have one line in Sanskrit and another in a regional language.
Prince Rama Varma has been singing bhajans, hymns, songs, … from several Indian languages.
Regards,
rajam