I am to wait / I am waiting - Tradução em português

I am to wait here for him. = I should wait here for him.

I am waiting here for him. = this is what I'm doing right now.

Acertei?

Os "here"s não deveriam estar no final das frases?

Yes, you're quite right.

On the first one, you could go stronger than "should" toward "must." You could say you have been directed or ordered to wait for someone at that spot. But should is well within the range. You know, a parent will say to a child: "You are to go to your room right now." (And when he doesn't promptly follow orders, the parent mutters, "What am I to do with this child?")

On the second, yes, it's a simple declarative.

Yes, you could put 'here' at the end. It works either way.

And the translations?

Obrigada, Henry.

The translations:

I am to wait here for him. -> Eu tenho que esperar ele aqui.

I am waiting here for him. -> Eu estou aqui esperando por ele.

*Important*: The position of "aqui" in Pt would change the meaning

Eu estou aqui esperando por ele. ("aqui" não faz muita diferença na frase, o importante é o fato de que vc está esperando por ele)

Eu estou esperando por ele aqui. (o fato de vc estar esperando por ele não é importante na frase, mas sim o "aqui"; seu locutor provavelmente achava que vc estava em outro lugar, por isso vc precisou enfatizar)

Does the same happen in En?

Your interpretations are very insightful. Yes, I can see what happens in Portuguese, and how we might change the word order to vary the message. Perhaps some of the same happens in English also. And we have still more options:

Here I am waiting for him.
I'm here waiting for him.

We can do some of that in speaking, of course, with the amount of stress we place on certain words, intonation, etc. When we write, we can't signal as much, so I guess we have to be more attentive to these seemingly trivial matters.