Harappan language

The Harappan language, also known as the Indus language, is the unknown language or languages of the Bronze Age Harappan civilization. The Harappan script is yet undeciphered; it has not even been demonstrated to be a writing system, and therefore the language remains unknown. The language being yet unattested in readable contemporary sources, hypotheses regarding its nature are based on possible loanwords, the substratum in Vedic Sanskrit, and some terms recorded in Sumerian cuneiform, in conjunction with analyses of the Harappan script.
There are some possible loanwords from the language of the Indus Valley civilization. ' or ' is the Sumerian name of a prominent trading partner of Sumer during the Middle Bronze Age. Its identification remains an open question, but most scholars associate it with the Indus Valley Civilisation. Asko Parpola identifies Proto-Dravidians with the Harappan Culture and the Meluhhan people mentioned in Sumerian records. In his book Deciphering the Indus Script, Parpola states that the Brahui people of Pakistan are remnants of the Harappan culture. According to him, the word "Meluhha" derives from the Dravidian words mel and akam. Parpola also relates Meluhha with Balochistan, which he calls the "Proto-Dravidian homeland". He also relates Meluhha with the transient word Mleccha, a Vedic word used to mean "barbarian" and used by the incoming Aryan speaking population for the native Harappan population.

Identification

There are a number of hypotheses as to the nature of this unknown language:

A prevalent hypothesis places it within or near the Dravidian languages, perhaps identical with Proto-Dravidian itself. Proposed by Henry Heras in the 1950s, the hypothesis has gained some plausibility and is endorsed by Kamil Zvelebil, Asko Parpola and Iravatham Mahadevan. A 2021 research paper published in Nature argues that Proto-Dravidian was spoken in the Indus Valley based on the Dravidian word for "tooth", as well as genetic migration patterns.
A "language isolate", i.e. a language with no living continuants. In this case, the only trace left by the language of the Indus Valley civilization would be historical substratum influence, in particular the substratum in Vedic Sanskrit.
Another recent proposal treats many Indus inscriptions as merchant marks used for trade administration rather than running text, in which case the surviving corpus would offer only limited direct evidence for identifying the underlying language or languages.

Multiple languages

The Indus script only indicates that it was used to write one language, but it is quite possible that multiple languages were spoken in the IVC, much as Sumerian and Akkadian co-existed in Mesopotamia for centuries. Jane R. McIntosh suggests one such possibility: Para-Munda was originally the main language of the civilization, especially in the Punjab region. Later, the proto-Dravidian immigrants introduced their language to the area in the 5th millennium BC. The Dravidian language was spoken by the new settlers in the southern plains, while Para-Munda remained the main language of those in Punjab.

Other theories

Michael Witzel suggested as an alternative, that an underlying, prefixing language similar to Austroasiatic, notably Khasi; he called it "para-Munda". Witzel argued that the Rigveda showed signs of this hypothetical Harappan influence in the earliest historic level, and Dravidian only in later levels, suggesting that speakers of Austroasiatic were the original inhabitants of Punjab and that the Indo-Aryans encountered Dravidian speakers only in later times. The theory was since further supported by Franklin Southworth.. As of 2019, Witzel prefers to leave the question of the original Indian language open until better reconstructions for Dravidian and Munda substrate components in Indo-Aryan languages have been done.
Indo-European languages: generally believed to be arriving after 1800 BCE, but recent genetic and linguistic study suggests that the language family emerged from the Fertile Crescent as early as 6000 BCE and likely spread to South Asia.