"He is in front of her."
Terjemahan:Dia berada di depannya.
Why not "adalah" when using a position (di...)? The verb is always "berada" or "ada" for positions?
Yes, you are right. Ada means exist, and position explains the existence (the place).
Of = dari. Diartikan secara implisit. Dia (berada) di depan (dari) nya.
You don't know who is "her". A baby girl, a woman, a girl, or even a female pet...
No, "is" is not an auxiliary word, it's a verb, and it's mandatory in English. No English sentence without a verb.