With scripting language I had something like jython in mind. It is indeed another code-layer ontop of java to interpret the scripts. And, not unlike python, its dead slow in some cases.
Someone reported about a factor of 100 for java against Ruby. jython is only 50. But this is still so bad that I would not waste my time.
You may be worrying too much about speed. Remember, a lot of people have written scalable web sites using PHP, so clearly a slow front-end language is not a big liability.
BRL uses Kawa Scheme, so the code is compiled to JVM bytecodes. The result is slower than C implementations of Scheme, but still faster than PHP.
I don't worry about speed, except we are talking about a factor 50 or even 100.
But one thing must be clear: The quick development that is possible with very high level languages is an advantage for the developers. They have quick time to market, fast prototyping etc.
The one who pays is their client!
This is indeed the wrong point of view!
I think it is desirable to give clients the best possible user experience and execution speed is indeed a valuable point, especially in the web.
A friend of mine still codes assembly if he feels its necessary. I 'am not that fanatic (in facts he is always making fun of java) - but, once you have used his number crunching algos, you'll never go back.
Scala usually results in much faster code then Java. Of course it isn't a "script" language in the usual sense, but are much more modern static and strong typed language (with functional leanings).
Someone reported about a factor of 100 for java against Ruby. jython is only 50. But this is still so bad that I would not waste my time.