Sanskrit shows no affinity to dravidian, unlike european languges even though dravidian being in its vicinity, is there any purana which discusses the differences between north-south india, or its totally alien languages in contrast to sanskrit? How did south indian languges came to be.
Here is a partial answer.
The Dravida word itself is a Sanskrit word as said by The Destroyer.
In Manu Smriti Dravida is simply mentioned as the name of a Vratya caste who used to be originally Kshatriyas but due to non-performance of Samskaras and sacred rites attained the Vratya status.
10.21. But from a Vratya (of the) Brahmana (caste) spring the wicked Bhriggakantaka, the Avantya, the Vatadhana, the Pushpadha, and the Saikha.
10.22. From a Vratya (of the) Kshatriya (caste), the Ghalla, the Malla, the Likkhivi, the Nata, the Karana, the Khasa, and the Dravida
To understand what this term Vratya means see the following verse from the same text:
10.20. Those (sons) whom the twice-born beget on wives of equal caste, but who, not fulfilling their sacred duties, are excluded from the Savitri, one must designate by the appellation Vratyas.
Regarding mentions of Dravida Desha, probably such mentions are found in Puranas like Bhagavata Purana (unable to find the exact verse now).
Here is a reference from the Bhavishya Purana:
After the demise of Vikramaditya of the Golden Age in Bharat, there were as many as eighteen Kingdoms named Indraprastha, Panchaala, Kurukshetra, Kampila, Antarvedi, Vraja, Ajmer, Marudhanva (Mawaad), Gurjara ( Gujarat), Maharashtra, Dravida (Tamilnadu), Kalinga (Orissa), Avanti (Ujjain), Udupa (Andhra), Banga, Gauda, Magadha and Kaushalya.