"I believe the holy grail of language learning is the ability to learn a language outside the country that speaks it, to a level of fluency that puts the user within 30 to 45 days of advanced reading, speaking, and vocal comprehension fluency once they are in the country." That sounds like an ambitious, but reasonable, goal.
The author notes, while writing in English, "I’ve independently studied the following languages and achieved varying levels of fluency. By competency:
1. Spanish
2. French
3. German
4. Swahili
5. Russian
6. Hindi
7. Farsi
8. Arabic
9. Afrikaans
10. Polish"
That list is heavy on Indo-European languages (with Swahili in the highest place for a non-Indo-European language) and rather heavy on closely cognate languages within the Indo-European language family that share many mutual literary influences. Learning Japanese or learning Tamil for someone who already knows those languages would be a good test of a new method.
AFTER EDIT AS EDIT WINDOW IS ABOUT TO EXPIRE: Yes, Arabic too is a non-Indo-European language
http://en.wikipedia.org/wiki/Semitic_languages
and as a Semitic language in the Afroasiatic language family different language family is quite a differennt language from Swahili (a language from the Niger-Congo language family).
http://en.wikipedia.org/wiki/Swahili_language
http://en.wikipedia.org/wiki/Niger%E2%80%93Congo_languages
My (partial but suggestive) list of languages studied before appears in my Hacker News user profile.