This is what I've been thinking lately i.e. C and Lua (throw in LuaJIT too if speed is needed).

But I've found out that using functional parts of modern C++ (bear with me) as a higher level language with C underpinnings also works very well. But you need tremendous discipline to do it successfully. For eg - using only C POD structs, no constructors, no exceptions, no inheritance, limited template usage etc. Some would say a very C style C++ with a lot of syntax sugar.