Going from Thai to Swahili (Kiswahili) has a composite linguistic distance of 78% (heuristic estimate). Below is the dimension-by-dimension breakdown.
Shared vocabulary, cognates, and loanwords.
Morphology, syntax, word order, cases.
Shared sounds and phoneme inventory.
Thai → Latin
Tai-Kadai ↔ Niger-Congo
The 5 languages with the lowest linguistic distance from Thai:
A quick 3-question check between Thai and Swahili. No signup.