Are there many English-only master's degrees in Taiwan for domestic students?

I find it hard to believe that the entire curriculum is in English.

Also, are there other examples of graduates programs here claiming to be totally in English, but actually having Mandarin in lot of the coursework?

Well, Tsing Hua has an English taught technology management MA.

I Shou university has a school for international medical students. And one for intelligent systems and automation.

More at: www.studyintaiwan.org

Often schools that get paid to host international students have such programs. The ones i have seen are indeed in.english, and some latin, as they are biology based. The lions share of students are all foreigners, so they tended not to revert back to mandarin. I guess it depends on school.