http://www.hkmdb.com/db/movies/view.mht ... ay_set=eng
A few years ago I added some cast names to Legend of Mother Goddess, taken from the not-very-clear screen credits. One of the names appeared to be Kwok Yi Yan, so I included that cast name. However, from the poster it's clear that the name should have been Tang Gok Yan (whom I also visually can now recognize in the film). So I have changed the cast name of Kwok Yi Yan to Tang Gok Yan for this film.

Database says it's Mandarin language.

It is a Taiwan movie and the old english subbed version is Taiwanese language:
https://www.youtube.com/watch?v=lUGDmL7o5ZM

There's also a remastered version in Mandarin:
https://v.qq.com/x/cover/kqpd5cpii12ubs ... elmt7.html

When I compare the audio tracks, I tend to believe that original language is Taiwanese, not Mandarin. Also, I find it strange to think that a Mandarin movie is dubbed into Taiwanese and I'm not aware of any example where this was the case.
Taiwanese audience should understand Mandarin as well, while Mainland audience would not necessarily understand Taiwanese. But with my poor knowledge I'm not authorized at all to claim Taiwanese dubbings are impossible.