One finds references to South India, called Dravida Desa during the Santana Dharma Period
There are references to in Tami literature and Sanskrit Texts, Vedas,Ramayan, Mahabharata,Eighteen Purans and in later Sanskrit and regional literary works.
Regional literature refers to Sanatana Dharma and Ithihsas in detail, e it Tamil, Telugu,Kannda,Bangla, Oriya.
Evidence abounds that a healthy trade between the people of the south and the north flourished since the Vedic period.
Now the question is how did these people communicate with each other in view of the fact that India has multiple languages and dialects.
There are 22 major languages in India, written in 13 different scripts, with over 720 dialects’ .https://www.justlanded.com/english/India/India-Guide/Language/Languages-in-India
‘According to Census of India of 2001, India has 122 major languages and 1599 other languages. However, figures from other sources vary, primarily due to differences in definition of the terms “language” and “dialect”. The 2001 Census recorded 30 languages which were spoken by more than a million native speakers and 122 which were spoken by more than 10,000 people’ -wiki
Sanskrit is said to be oldest language being dated about 5000 years back.
( I had written this my not be correct and Sanskrit might be much older along with Tamil, an ancient language of India. million year old Tamil Site near Chennai ,Tamil Nadu with advanced Tamil civilization.And Tami quotes Vedas and Vedas in turn quote Tamil and Tamil Kings.Please read my articles on this)
The languages spoken in the south and even among the north indi differ.
Sanskrit is accepted in all the regions though!
Groups in India spoke different languages.
Yet they were in intimate contact with the Sanatana Dharma People whose language was Sanskrit.
Not all groups were familiar with Sanskrit.To compound the issue there was Vedic Sanskrit and Panini Sanskrit ( Ashtdhyayi)
Vedic Sanskrit is the language of the Vedas, a large collection of hymns, incantations, and religio-philosophical discussions which form the earliest religious texts in India and the basis for much of the Hindu religion. Modern linguists consider the metrical hymns of the Rigveda to be the earliest. The hymns preserved in the Rigveda were preserved by oral tradition alone over several centuries before the introduction of writing, the oldest among them predating the introduction of Brahmi by as much as a millennium .
The end of the Vedic period is marked by the composition of the Upanishads, which form the concluding part of the Vedic corpus in the traditional compilations, dated to roughly 500 BCE. It is around this time thatSanskrit began the transition from a first language to a second language of religion and learning, marking the beginning of the Classical period’
And Tamil a past of not less than 20,000 years at a conservative estimate..the excavation of Poompuhar confirms the date.please read my article on this.
There are references to the effect in Sanskrit Texts, Mahabharata and Ramayana to Tamils.
Udiyan Cheralathn, a Tamil King provided food to both the armies during the Mahabharata battle.
Shiva is considered to be the founder of Tamil language.
Agstya, Subrahmany are associated with Tamil intimately.
Lord Krishna and Arjun married Tamil Pandyan Princesses;Krishna had a daughter and had her married to a Pandyan prince.;Arjuna had a son from south.
Sahadeva went on a pilgrimage to south and Balarama came to south and worshiped Subrahmanya.and of course, Parshurma who founded the present Kerala State.
I can go on adding in this vein.
But the issue is, how did these people communicate with each other?
The common thread seems to be Brahmi.
By Anonymous – Commentary: The Devimahatmya cropped from http://www.nb.no/baser/schoyen/5/5.20/ms2174.jpg; taken from: w:en:Image:Devimahatmya Sanskrit MS Nepal 11c.jpg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=191227
Brahmi (brāhmī) is the modern name given to one of the oldest writing systems used in South and Central Asia during the final centuries BCE and the early centuries CE. Like its contemporary, Kharoṣṭhī, which was used in what is now Afghanistanand Pakistan, it is an abugida.
The best-known Brahmi inscriptions are the rock-cut edicts of Ashoka in north-central India, dated to 250–232 BCE. The script was deciphered in 1837 by James Prinsep, an archaeologist, philologist, and official of the East India Company. The origin of the script is still much debated, with current Western academic opinion generally agreeing (with some exceptions) that Brahmi was derived from or at least influenced by one or more contemporary Semitic scripts, but a current of opinion in India favors the idea that it is connected to the much older and as-yet undeciphered Indus script…
The Brahmi script diversified into numerous local variants, classified together as the Brahmic scripts. Dozens of modern scripts used across South Asia have descended from Brahmi, making it one of the world’s most influential writing traditions. One survey found 198 scripts that ultimately derive from it.
The script was associated with its own Brahmi numerals, which ultimately provided the graphic forms for the Hindu–Arabic numeral system now used through most of the world.’
Tamil Brahmi was discovered in Harappa and there is a Million year old Brahmi script found in Karnatka, Kannada Brahmi.
Brahmi script, though associated with Sanskrit was also used in other parts of India with local variations.
We have another,Brahui, spoken by Tamils and by the people of North Weaste India!
‘Brahui /brəˈhuːi/ (Brahui: براہوئی) is a Dravidian language spoken by the Brahui people in the central Balochistan region ofPakistan and Afghanistan, and by expatriate Brahui communities in Qatar, United Arab Emirates, Iraq, and Iran.It is isolated from the nearest Dravidian-speaking neighbour population of South India by a distance of more than 1,500 kilometres (930 mi). Kalat,Mastung, and Khuzdar districts of Balochistan are predominantly Brahui-speaking.
By BishkekRocks – Base map template: demis.nl. Sorce for map data: Language families and branches, languages and dialects in A Historical Atlas of South Asia, Oxford University Press. New York 1992., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1593835
Tamil Chola King, ancestor of Rama, who built the Thiruvellarai Temple, near Sri Rangam, ruled from the present Pakistan region.
We have yet another common Link language,after the advent of Buddhism.
It is Pali .
Pali is the Middle Indo-Aryan language in which the Theravada Buddhist scriptures and commentaries are preserved. Pali is believed by the Theravada tradition to be the same language as Magadhi, but modern scholars believe this to be unlikely. Pali shows signs of development from several underlying prakrits as well as some Sanskritisation.
The prakrit of the North-western area of India known as Gāndhāra has come to be called Gāndhārī. A few documents written in the Kharoṣṭhi script survive including a version of the Dhammapada.
Considering these facts it seems logical to conclude that .apart from Sanskrit, Prakrit,Brahui and Pali were used as common link languages of India since Vedic Times.
They have changed during the course of Time.
References and Citations.