The Treaty of Hidalgo recognizes Spanish in the purchased territories.
As a junior high student transferring into a San Diego junior high school from a northern Virginia high school, I saw that in action. My Spanish teacher in Virginia was teaching Castilian Spanish. The teacher in San Diego was supposed to be teaching Mexican Spanish. Because it was compulsory to teach the course, the room was full of people who really didn't want to be there. The teacher didn't want to be there either and often slept through the class period.
When I signed up for German in high school, my teacher was a native German speaker from Karlsruhe, Germany. My spoken German reflects her influence and was noticed by my German customers in Frankfurt. The Duolingo voice recognition gets particular about trailing 't' sounds. It's the only thing that I get frequently tagged for "failing".