Spanish?.....why not Cantonese?........or Arabic?..........or Urdu?..........or Swahili!..........
and about the other 700+or so languages in this planet?
Because. The Spaniard bigots wouldn't stand for that.
They aren't cultural liberals who seek abstract multiculturalism. They're nationalists who seek to replace the language of this country - which they despise - with the language of the countries and nations that they identify with - the Spanish speaking ones!
There is no movement in Mexico, or South America, or Central America, and definitely not in Spain to replace Spanish or even to allow different languages to co-exist. Hell, they have running battles over the use of Spanish dialects in those countries. Try advocating the use of English in a Mexican political campaign and see how long you live. That's how serious they take it.
The multiculturalism crap is just camoflauge for the real intent: take over and supplant the hated Gabacho culture and hegemony with Latin American culture.
Only get the Anglos to pay for it. That's a key point.