Is this an expression in fluent Spanish? Because the English translation is completely awkward... it would never be uttered by a fluent English speaker except to make fun of someone struggling with English. There are lots of ways to express this idea in English, this just isn't one of them.
I've heard that rostro usually refers more to one's physical face and cara is more like the overall appearance of the face. For example, you apply lotion to your "rostro" and your "cara" has a look of surprise. Can't confirm this with any source. They're mostly if not interchangeable, though I'd say cara is more common. There are also certain phrases/idioms that use "cara" and would sound odd if you used "rostro" instead (I.E. cara a cara). Hope that helps!
Okay guys im native spanish from spain his face shows happiness would be translated thus
Su cara muestra felicidad.
La cara de muestra felicidad only would be used in a context in which there are a girl and a boy or in one in which there are many people and like u point one or like u select one and u say la cara de el ....
Su is for él and ella and for usted(the formal way of tú) for they ellos we have sus