Historically, those taxes had been used to pay for wars and other acts that were used to spread Castillian in regions it was not spoken. Both in the Peninsula and South America.

Nowadays, taxpayers money funds institutions that preserve and promote Castillian.

Maybe don’t try to kill languages and life support won’t be needed.

Also, it makes more sense to spend in preserving something fragile than to promote something already popular and strong.

I am inclined to think it is not the taxpayers money that you are after