For holiday pay, legally, the question is not whether the worker is foreign but whether the job is subject to the Labor Standards Act. The Ministry of Labor maintains that list (somewhere).
In the current (2020-6-10) version of the LSA, the list of applicable holidays is no longer kept in the Enforcement Rules of the LSA. Instead, LSA Art. 37 gives the Ministry of the Interior the authority to decide which holidays are worthy of being days off. The MOI’s list is here, and in Art. 4 we can see four consecutive days for CNY (1 day for 除夕 and 3 days for 春節, which would be the 初一 to 初三 of OP’s screenshot). In accordance with LSA Art. 39, the employer must pay the worker’s wages as usual for these (and various other) days, and if the worker agrees to work on these days, the employer must pay double.
If both parties agree to swap holidays for regular days, that’s fine, but then the substitute holidays are subject to the same rule: regular pay or double pay. For part-time workers, it’s more complicated (I’m sure there’s a thread somewhere…).
Of course, if the working person is not a worker (勞工) in the legal sense, the LSA flies out the window, but in general this will not be the case for a large company with a large workforce, unless the job in question is not on the MOL’s list.
As for these (apparent) bonuses, if they are “special payment for Spring Festival” (春節⋯給與之節金), then under LSA-ER Art. 10 Subpar. 3, they do not count as part of the wages. (They won’t be “year-end bonuses” i.e. 年終獎金 as in Subpar. 2 because that refers to the bonus calculated from the employer’s annual profit, but if they were they would also be excluded.) On the other hand, if these payments do not qualify as Subpar. 3 “special payments”, it seems they must be wages, even if the employer calls them bonuses (LSA Art. 2 Subpar. 3).
Whatever the payments are, if they are prescribed by the worker’s contract, the employer has a good cover story (“they just didn’t negotiate hard enough to get the higher tier of CNY bonuses”). If the contract simply states that the payments will be determined by Party A, the cover story is still there, but the screenshot makes it look dubious. If the contract says nothing about these payments, then it’s hard to spin this case as anything other than discrimination on the basis of nationality.
If the contract itself doesn’t determine the calculation of these payments, but the work rules do (with the same wording as in the screenshot), then because the work rules are supposed to apply to all workers, the employer can’t reasonably claim that anyone is subject to the discriminatory rule because of failure to negotiate out of it.
As a starting point, I would contact the local labor department (whichever city the workplace is located in, or any of the multiple cities where the company employs foreign workers, as the case may be). A complaint may be submitted anonymously (i.e. the labor department knows who the complainant is but isn’t allowed to tell the employer without the complainant’s permission). If you’re not employed by the company, there’s no point in mediation, but you can still ask the section of the department dealing with labor standards inspections to look into it.
If that doesn’t go anywhere, the Control Yuan might take an interest, and you can probably find an NGO that would be interested.