In some place I read that differences in languages could account for at most 30% of improvements in speed of development. This is an epsilon if compared to differences between programmers.<p>Another issue is that, if you are talking about small-to-medium sized applications then clearly there is a difference in languages. For example, it is pretty clear that writing a script is easier in perl than in C, or writing a medium sized expert system is easier in LISP than in Pascal.<p>However, if you consider large scale applications (100k+ LOC), then I don't believe there is any difference between writing in C, C++, Java, or Common LISP, as long as the programmer(s) have deep experience with the used language.<p>Just notice that the language is not going to solve the large-scale problem by itself. As long as such language has tools for creating abstractions, the code will have about the same complexity no matter what. If that complexity will be encapsulated in simple concepts (structs and functions) or higher level concepts (closures and continuation) depends on the taste of the developers and the language used.