What's the use of this project? A shell language bears the main purpose of enabling user to interact with the system including it, and thus the shell is platform specific at it's nature. A language may well be compiled to both Windows and POSIX shell languages, but what will happen when a feature or a program endemic to one of these systems is invoked within a shell script? Is there a complement in Windows land for, say, sed(1), awk(1), ls(1), cp(1)? If so, are these programs synonymous. What will happen when I invoke ls in my program, will it get translated to dir for windows?
Shell languages' primary purpose is invoking programs. Most important programs for shells are endemic to one platform or another, and thus translating only the shell language does not mean anything.