Question

How many spaniards speak castilian spanish

Answer 1

Almost every Spaniard. As there are 46.5 million Spain population, I would say 46.5 million (or the closest to that)

Answer 2

It is near impossible to tell. First of, some corrections: Castilian is Spanish. Castilian is the original name of the language, the only name it had before Spain was created at the end of the Spanish succession war. It was renamed afterwards in order to push it as the only “national” language of the whole empire. But 46.5 million speak Castilian Spanish.