You pronounce it "ta-kay" which rhymes with "okay". Apparently William Shatner kept on calling it "ta-kai" (rhymes with his popular catchphrase "oh my!") even when George went over and over with him it's Takei, but "ta-kai" is a legitimate Japanese word.
Comments
Tack Kay.
But is it Tack-KAY or TACK-kay?
Seems I was wrong.
fffff
That's how I've always said it and I do believe it's correct.
If this were the X Factor, it would be straight Tacky (excuse the pun)!
I asked George himself and I got a ta-kay from him. He also says it himself here