Why was Zsaji not given the knowledge of English?

An answer to this question necessarily requires some speculation, since we don't know whether the placement of Zsaji's village on Battleworld was a conscious choice on the Beyonder's part, or whether it just happened to be pulled along for the ride when he constructed Battleworld from those planetary fragments he threw together.

Even if it was a conscious choice on his part, we can't be sure what the thought process behind that decision was. Captain Marvel (Monica Rambeau) assumed that the Beyonder wanted the alien villagers there as "innocent victims". For all we know, she could've been right about that, but then again, she could've just as easily been wrong. It's all guesswork.

Marvel Super Heroes Secret Wars #4

The main utility Zsaji offered to the Earthly combatants, though, was her power of healing. So if we assume, for the sake of argument, that the Beyonder consciously placed her on Battleworld for that specific reason, then she clearly served her purpose, despite her inability to speak English. It's not so much that it was favourable for her not to speak English, as it just didn't matter in terms of what she was there to do.