You may notice that I usually spell my martial arts by the Wade-Giles method rather than the spelling most commonly used by people who consider themselves very "serious" about Tai Chi.
The pinyin method of translating Chinese words was developed in the mid-20th Century by the Chinese government. It's the most commonly used method now.
But the Wade-Giles method of spelling and pronouncing Tai Chi caught on before the pinyin version, which is Taiji. I use the Wade-Giles spelling of Tai Chi Chuan rather than the pinyin method of Taijiquan.
I'm not the only one. Even T'ai Chi magazine uses the old way of spelling the art.
That's not why I do it, though. I use "Tai Chi" because that's what Americans know. Most Americans seeing the word "Taijiquan" will not realize that it means "Tai Chi." And they have a hard time using the "ch" sound when reading the letter "q."
Hsing-I has always been a challenge. Xingi is also a logical way of spelling this art, but it isn't as well known as Tai Chi so I don't worry about it. I use the Baguazhang version rather than Pa Kua Chang because it more accurately represents the pronunciation from an American perspective.
I wanted to clear this up. It would be nice if everyone could use the same spelling, but until Americans understand that Taijiquan means Tai Chi, I'll continue to use the Wade-Giles spelling just to make it easier for newcomers to understand.