You are asking for a lot of things from the framework; network enabled, multi-platform, multi-language, high performance (which ideally should be further specified - what does it mean, bandwidth? latency? what is "good enough"; are we talking kB/s, MB/s, GB/s? 1 ms or 1000 ms round-trip?) Plus there are a lot of things not mentioned which can easily come into play, e.g. do you need authentication or encryption? Some frameworks give you such functionality, others rely on implementing that part of the puzzle yourself.
There probably exists no silver bullet product which is going to give you an ideal solution which optimizes all those requirements at the same time. As for the 'additional' component of your question - yes, if you restrict language requirements to python only, or further distinguish between key vs. nice-to-have requirements, there would be more solutions available.
One technology you might want to have a look at is Versile Python (full disclosure: I am one of the developers). It is multi-platform and supports python v2.6+/v3, and java SE6+. Regarding performance, it depends on what are your requirements. If you have any questions about the technology, just ask on the forum.
