I’ve been going through the Messenger Series by J.N. Chaney. It’s trash sci-fi, more than a little contrived in spots, and you really don’t want to go digging into, well anything about it, too hard. That said, it’s what I’ve been in the mood for, for the last little while and it’s often quite funny. Basic plot of the series is that an idiot finds an ancient jaeger, left behind by a long dead race, and must now face off against that race’s mortal enemy to save all life in the galaxy.
Fastest? Moving to a Spanish speaking country. Total immersion is how the French Foreign Legion teaches French from my understanding.
I would probably do a mix of a language program, say Duolingo, Pimsler tapes or Rosetta Stone, and asking a few of your Spanish speaking friends to speak primarily Spanish to you, switching to English only when you are completely lost on a concept. Between the two you should pickup Spanish or rather, their dialect of Spanish, fairly quickly.