Going from Tamil to Zulu (isiZulu) has a composite linguistic distance of 86% (heuristic estimate). Below is the dimension-by-dimension breakdown.
Shared vocabulary, cognates, and loanwords.
Morphology, syntax, word order, cases.
Shared sounds and phoneme inventory.
Tamil → Latin
Dravidian ↔ Niger-Congo
The 5 languages with the lowest linguistic distance from Tamil:
A quick 3-question check between Tamil and Zulu. No signup.