One should also note that “assistant” is a vague term.
Since every other organization that’s tried to do it has been shut down, I’ll provide this example: In Fulbright Taiwan, the English Teaching Assistant program “requires” “coteaching” and “assisting” a local teacher in the local teachers’ classroom activities. What ETAs often end up doing, however, is teach their classes completely alone, sometimes under the supervision of a non-English speaking other person in the school, who may or may not be paid for their time. When they are “assisting” a local teacher’s own classes, often that local teacher is themself an “assistant” (speaks some English but hasn’t a clue how to teach). Not great when you’ve just graduated from college and majored in art history or underwater basket weaving/ didn’t come in with any teaching experience / wanted to go abroad for a year for the resume and didn’t expect so much work.
I would say regardless of laws, first time teachers had best get some experience teaching from a program that trains them (like a cram school with a good reputation or a teaching license program in one’s home country) cuz being thrown in the deep end in Taiwan isn’t great for learning how to teach well.