Ask HN: How does a developer learn a non formal language?

I'm a developer and I want to learn German. There is a plan, a deadline, motivation and hopefully time to do it. Basically, I'll try to reproduce what I did to learn English (native Spanish speaker) but in a shorter period of time. I have to said, my English is still far from perfect but I can watch movies and the like and understand about 80% of them, I can communicate effectively in my area of domain (software development) and in other common areas (but cannot talk about politics or geology, for example). I would say my level of English is something between B2 and C1 (https://en.wikipedia.org/wiki/Common_European_Framework_of_Reference_for_Languages)

So, this is my plan:

July, August and September (2016): Learn the basics, the grammar, watch Youtube videos with German subtitles. I have bookmarked a couple of grammar books and good Youtube channels.

October (2016) to July (2017): I'll be in Germany, this means I'll have to speak! Although what I'm going to do there only requires me to speak English. Will keep improving the grammar and will keep watching, not only videos, but also the TV and the radio and of course I'll talk with German people.

The level I want to reach is the same as my level of English I have now. I know it's a hard task to accomplish, but boy, I'm motivated.

Suggestions, tips and personal experience learning non formal languages are welcome. Thanks!