This idea makes sense, (even if the site sounds like it's empty and poorly designed), but only if you are comparing similar languages. For web scripting, I learned PERL first, and recently made the switch over to PHP for most of my new website stuff. Due to the old stuff still needing periodic work, I'm constantly going back and forth between the languages, and a cheat sheet showing me the syntax diffrences and basic fundamentals is invaluable for me.
Even if this site was fully fleshed out, you would still never get past the initial learning curve of a new language with just a list of ways to do all the particular tasks. It would be useful while learning it, but you still have to learn the new language.