This is going to suck, because you’ll need to pay the non-resident rate of 18% (I think) with no deductions or exemptions. From what I understand, that’ll only be for the salary component paid while you were in Taiwan though.
The tax office has a list of required documentation, but I’ve found them to be quite flexible if you can’t fully comply (my attitude was along the lines of “this is what I have - do you want the tax or not?” ).
).