Should I now python the box to learn Java or C++?

With and With++ very difficult. Especially after the super-high-level language. Java can be a normal occurrence in this area. But, for me, for not sverhsekretnye web server-side python is perfect. Django is now growing and popularities can soon expect many vacancies.

Can about yourself to tell. On PHP a couple of years wrote then (and now) in Python for a year with a small write...
\r
Recently Erlang fiddle — a great thing for their tasks. You can study for 2-3 weeks to a sufficiently good level. Even now in most large web applications using Comet connections, and if in the future, WebSockets will be included in the use, in this case the Erlang-perhaps no equal. His fiddle and postponed for the future.
\r
And in the nearest future I think C study to... writing extensions for Python or any other PL))
\r
About C++ I doubt that this web-serverside anyone (except Google in rare cases). So learn Java/C/Ruby and Python in parallel, dig down, in the same Twisted for example.

The words "web server-side" and "C++" does not tally practically nothing.

In General, to go to Java definitely worth it, now an acute shortage of Scala developers - there are good courses on coursera. Get familiar with the Typesafe Stack and Play2 framework. Lift had become obsolete. Everything that erlang can only Akka... this is scala/java with all the subsequent advantages and disadvantages. Take a look at the Apache Direct Memory and Stack Allocator to address the delays in garbage collection.

C++ is good if you are going to sit in one position for 5+ years, and have a stable salary. C++ is now very popular in the robotics/hardware with all computer visions, etc.

Now VEB goes smoothly in Java, so that jobs will be much more in the future.
Enterprise potikha otlamyvayut from Beraucracy Driven Development's, and J2EE is not at all in fashion.

Go now specifically lacks good libraries, frameworks and ORM's, while runtime there is quite edible. Think how to write MVC framework under Go.

C# - I'm not a cat burglar, and wild mono slag. Xamarin there.

Inside Twitter is written in Scala — same as Java, but higher level, with a slight touch of functionality. After Django it can be more comfortable to read than Java. There are plugins for different ides, but more adequately work with the idea and nevinson. Has a web framework called lift. Documentation is not yet so much as "classical" languages, but gradually moving in the right direction

Java vengeance will write the application under Android. If you want a smooth transition, better than Java, since the level of abstraction higher. C++ just have a lot to load in the head of the new pieces.
\r
And another thought, the language is nice, but without a platform it's not worth much now, so it's better to learn from something applied, and preferably immediately start to use it, and it will be forgotten quickly.