I think my only hope for learning Spanish at this point would be a game that starts out in a Texaslike setting, with the storyline missions sending the player into progressively more Spanish-speaking situations, with more Hispanic-specific cultural elements, until complete immersion occurs.

Start out ordering tacos for lunch. End by smuggling someone out of Venezuela via the Orinoco in a narco-submarine, with paramilitary groups ready to execute you if you mistranslate something.

Well, you're wrong. You can learn stuff "truly" without it being fun. There is a lot of stuff people learn without having fun doing it.