A multicultural person may be bilingual or multilingual (individual effect) and this may make them more marketable
for some careers (causal). Sometimes, for example in American society a person is judged on their accent (causal) and may be discriminated against based on the effect side (individual’s accent).
Multicultural psychology studies more of the detail. While, social psychology allows us to stand back and look at society in broader sweeps. Of course, there are times that they overlap as you point out.
What are some specific areas in society that you can use as examples to compare multicultural and social psychology?