Assuming you have the most efficient code possible, the efficiency and speed of the interpreter can still affect the ability to scale an app.
Another thought is, the interpreter may or may not have scaling / clustering available, be it through a built-in functionality or an external queue or something.
Sometimes we have to code around interpreter/speed issues. I work in the JVM languages sometimes. I have to do things differently directly in Java if a particular JVM language I use isn't cutting it. Same goes for ".NET", which is over 30 some languages.