Whether you say "tea" or "chai" reveals the trade route.
Almost every language has one of two words for tea. "Cha" from Cantonese and Mandarin travelled overland: Persian chay, Russian chai, Arabic shay, Hindi chai. "Te" from the Min Chinese of the port province Fujian came on Dutch ships from 1606: English tea, German Tee, French thé. The exception: Portugal says "chá", having bought tea via Macau since the 1550s.
Useful: A word can be a map: land and sea routes leave different vocabulary behind.
Source: en.wikipedia.org