“Chai” doesn’t mean “tea” in English though - it signifies a specific type of mixed-spice tea. “Chai tea” is no more redundant in English than “Earl Grey tea” is.

One a word has been borrowed into another language, the meaning/etymology of the word in the source language is irrelevant. For example, I bet when you say “sushi” you mean “fish on/wrapped in rice” and not the vinegared rice itself, because that’s what it means in English. Similarly, when a Japanese speaker says “mansion”, they mean a high-rise apartment or condominium, not a large house, because that’s what the word means in Japanese.