"Mike is a new Dutch translator."
Translation:مايْك مُتَرْجِم هولَنْدِيّ جَديد.
Since this is the beta version and there is a lot about DL [DuoLingo] Arabic that needs work, it's good to give them feedback. But to respond to your point: I assume that with DL any course that we have to supplement with additional material (grammars, online stuff).
It's an interesting question that reveals that you may know Hebrew, since modern Israeli Hebrew uses the pronoun for copula. In looking into it, the "zero copula" wiki entry states that "when both the subject and the predicate are definite, a pronoun (agreeing with the subject) must be inserted between the two." The example given is محمد هو المهندس (Muḥammad huwa l-muhandis), "Muhammad is the engineer' (lit. "Muhammad he the-engineer"). So, in this case, since the predicate is not definite, we don't use هو here as far as I can tell, but I'm just a learner. Thanks for asking this question & we can see if a native Arabic speaker replies. The use of the third person pronoun in such "equative" nominal sentences is discussed here: http://www.llf.cnrs.fr/sites/llf.cnrs.fr/files/evenements/colloques/DG_copula.pdf