Common Language Implementations in MPS: Haskell OCaml Scala PERL GO D C/C++ Objective-C Kotlin Groovy Python PHP C# Lips Scheme Lua etc

For C, there is mbeddr (see mbeddr.com). A C# implementation started some years ago but seems it's currently not under active development :(.
A Lisp implementation would be a nice exercise I guess, because Lisp is a very small language. I don't know of any other implementations but I must confess I didn't get the point of having common languages as MPS implementations.

This is the only way you can test the robustness and completeness of the framework.

You need to ensure that may language idioms can be modeled succinctly and optimally. This can form the test suite.

Also FOSS programmes in these languages can be compiled and bench marked.

Also this will help develop new languages using these implementations.

This is the best way to test the metal of mps and get ideas for improvement

I would like to have an answer for this question, as well.

This could also serve as one of the validation and test suite for the MPS. If some of these languages cannot be implemented then this is not a holistic framework to base a new language development on other than for non critical use cases. Also other back end support like .NET, LLVM, Custom LLVM, direct native.