1. https://indianexpress.com/article/india/more-than-19500-mother-tongues-spoken-in-india-census-5241056/
2. https://www.jagranjosh.com/general-knowledge/most-spoken-languages-in-india-by-number-of-speakers-1541764100-1
3. https://www.statista.com/statistics/266808/the-most-spoken-languages-worldwide/
4. https://www.englishclub.com/learn-english/language-skills.htm
5. Jakobson, Roman, Gunnar Fant, and Morris Halle. “Preliminaries to Speech Analysis: The Distinctive Features and their Correlates”, MIT Press. 1976