You can teach English in Taiwan with just a university degree. That will be enough for you to receive an ARC (essentially a work permit/ temp residency card). Now whether the immigration department/education department will make a distinction between you working at an international school or not is another thing.
I think it is likely that the school you are applying for has a policy of only hiring people with the necessary licences and teaching degrees.
If you have your heart set on Taiwan, then you can immigrate here without securing employment beforehand and teach English without the licence. Maybe you could do an online Masters or get whatever certification your country/state whilst living in Taiwan.
quickest certs sufficient for Taiwanese visa requirements
Discussion
@damok
The LW already has a doctoral degree in literature, and has since completed requirements for a MA preliminary credential.
The MOE has no position on credentialing requirements for ISs. A bachelors degree is sufficient to meet the requirements for an ARC and work visa. I would agree the requirements are likely those of the ISs policy, in which case they really arent anything if the recruiter/leadership wants to hire the LW.
The LW already has a doctoral degree in literature, and has since completed requirements for a MA preliminary credential.
The MOE has no position on credentialing requirements for ISs. A bachelors degree is sufficient to meet the requirements for an ARC and work visa. I would agree the requirements are likely those of the ISs policy, in which case they really arent anything if the recruiter/leadership wants to hire the LW.