I may have a contrarian opinion: a new language, beyond certain level, does not increase productivity tangibly for a large enough team. Specifically, Scala does not necessarily offer more productivity than Java. It is a pleasure to write program in a language with more powerful features, for sure. It's just that bottlenecks of project are usually not language features, but core algorithms, system designs, meticulous testing, conflicting requirements that demand careful trade-offs, availability of robust libraries and frameworks, maintainability of the most complex part of the system, and availability of qualified engineers. Few of such bottlenecks can be removed by switching to a language like Scala.