Optics not logic. Knowing many languages is a sign of globalist sympathies.
Cruz shouldn't speak Spanish in public during the campaign for the same reason Rubio shouldn't be singing show tunes.
Optics.
He was raised by a Cuban father. Of course he knows some Spanish. I speak French, learned in an American high school. I consider it a good thing. He also has to appeal to a Hispanic base as much as possible. Many are legal you know.
I'm the most pro-American, conservative person I know.
No a big show tune fan, though.