Malcolm Gladwell wrote in "Outliers" that a person needs to invest 10,000 hours of concentrated and reflective practice to achieve mastery - which means it's going to take most developers 10 years just to attain mastery just through practice.
Back in the early 90s I used to work for Borland Australia, and I started as most developers do in online tech-support, this was in the era of a free 1-800 support number and I was one of 2 techs handling Language support calls for the whole of Australia and New Zealand. We would handle around 300 support calls each a week, that could cover absolutely any facet of Borland C++ or Turbo Pascal but were rarely easy even to the experienced developer. It was here that I learned the one true short-cut to Language mastery, and I'll pass it on to you here.
Teach someone else a thing, to master it yourself.
So given that we probably don't all have access to 300 gnarly C++ questions a week to keep us on out toes, how then to push oneself toward mastery. One way that Dustin Campbell (Microsoft VB PM, F# Master and formerly Coderush dev) discovered when he was learning F# was to blog about it on http://diditwith.net/ thus helping teach others how Functional Programming works and in particular how F# works. Dustin is well known these days as a master of languages, and I suspect that the exercise of blogging was instrumental - not just as a PR exercise but as a way to solidify his own understanding through teaching. I can't know whether that helped during his Microsoft interview process, but the effort we spend to teach others does return karmicly in interesting ways.
So what I suggest is, if you aspire to become a master in less than 10,000 hours - teach other developers. You could do a lot worse than Blogging about say your favorite C# or Delphi language feature, or to show off a feature in a Devex component or tool that you have recently learned about. In fact if you do the latter, I'll make sure to blog about your blogging and make sure that you get some people on your site to ask some gnarly questions.
Speaking of which, here are 2 great examples
Go on their sites and ask them some tough questions 