The core framework can be C/C++ (and let's be honest, C/C++ can be compiled and run everywhere). The core framework can also embed the V8 JS engine. V8 is the fastest of the three vendors' engines. It's not even using full JIT, its compiling to native on the first pass (if I remember the numbers right, it's something like 1 mb of code in 200 ms).
Since all successfull game framework is using a scripting language, let it be JS !