The advantage of doing a "language X to CL" translator is that it's going to be much simpler than doing it in another language (the number of features offered by CL is a huge superset of that available in any other language; the only exception is continuations), the result will be faster (the example Ruby translator is faster than Ruby, cl-javascript is faster than SpiderMonkey, etc, mostly due to SBCL being a reasonably good compiler), and you will have access to really good debugging tools (Clozure is really good at this - see http://openmcl.clozure.com/ccl-documentation.html#watched-ob... for example).
The advantage of doing a "language X to CL" translator is that it's going to be much simpler than doing it in another language (the number of features offered by CL is a huge superset of that available in any other language; the only exception is continuations), the result will be faster (the example Ruby translator is faster than Ruby, cl-javascript is faster than SpiderMonkey, etc, mostly due to SBCL being a reasonably good compiler), and you will have access to really good debugging tools (Clozure is really good at this - see http://openmcl.clozure.com/ccl-documentation.html#watched-ob... for example).