"I ask for a mango"

Translation: Ninaomba embe

[billhatcher]

Not sure, but I think "Naomba embe" should also work?

[a.l.i.a.s.]

Is ninaomba a frase that is actually used in speech? And if so, how?

[IndianaJBird]

Yes, it can be used to request something.
While at a restaurant we would say something like this
“naomba kuku na chipsi”
It is understood as “ I would like chicken and chips”
It also means to pray which is essential politely asking for something. In conversation it is permitted to remove the ni infix but only in the present tense.
It could also mean I am praying.

If you said “tuombe” it would mean “let us pray” when na is removed and the a changes to e it becomes a polite command.