Funny, because English is not my native language, but I would have no idea what the different meanings of 'that' would be.
Indicative that: "Which apple do you want?" "That apple." "This apple?" "No, that apple."
Causative that: "Why did you go to school?" "So that I could study Japanese."
Antecedent that, where that takes the place of some concept which has come before: "Did you study Japanese?" "That is a given."
"Never going to see it outside of literary constructions" that: "That which cannot be seen is more real than that which cannot be felt."
Adjectival-clause-introducing that: "We are looking for two students that are studying language pedagogy."
etc, etc
English grammar, fun stuff.
Fascinating stuff!
'Which' wouldn't be used here because 'are studying language pedagogy' is restricting/filtering 'students', and so it's essential to the meaning of the sentence. 'Which' is used for clauses that add non-essential information.
My shirt that is red is upstairs.
My shirt, which is red, is upstairs.