Polyglot: How I Learn Languages (Kato Lomb, pdf)
tesl-ej.org
tesl-ej.org
Despite not having any notable success with foreign languages until after completing her PHD in chemistry, she became a simultaneous interpreter of Hungarian. Russian, English, French, and German. She also did technical and literary translations in Italian, Spanish, Japanese, Chinese, Polish, Bulgarian, Danish, Latin, Romanian, Czech, and Ukrainian. Her approach only represents a single data point, but it's well worth reading for anyone interested in SLA.
I am a little in awe of people who speak multiple languages with ease. I struggle to learn any informal language other than English, my native tounge. There is something in my brain that blocks my attempts to learn human languages. I do not struggle with programming languages, just human ones.