It is said the same way. Swahili doesn't distinguish between present simple and present continuous.

I'm not sure if it is grammatical is Swahili, but even if it is, I would translate that more like "I am talking to you." Na literally means with, whereas your sentence makes "you" an object.

(Ku)zungumza = to talk

The rule is you always lose the "ku", the same way you lose the "to" in English

E.g. Nina(-ku)zungumza = I (-to) talk

*EXCEPT when the verb is a one syllable verb ,in which case the kind "ku" keeps the lone syllable company.

E.g. (ku)la = to eat, Ninakula= I eat

Linguists have fancier ways of putting it, but that's how it works.