You missed the point.
It had nothing to do with speaking Spanish being a good thing. It had everything to do with Cruz proving that he knew what Rubio said in Spanish and that Rubio was a lying.
SEN. MARCO RUBIO (R-FL): I don't know how you know he knows what I said on Univision 'cause he doesn't speak Spanish. And second of all, (LAUGHTER) the other point that I was-
That's when Cruz spoke Spanish.
Thanks for trying to explain. I’ll have to go watch that videoclip to get the full context.