I work at a company that exclusively uses Scala for the backend of our applications/services, and I found that if developers are willing, it's almost never a pr

I work at a company that exclusively uses Scala for the backend of our applications/services, and I found that if developers are willing, it's almost never a problem to have them learn Scala within a reasonable amount of time, if they come from a Java background. We found that it's very hard to find Scala developers when hiring, so we basically dip into the Java pool and look for strong and talented developers there, that are eager to try and learn Scala. We then train them on the job, which almost never takes more than a couple of weeks before they really become productive. So I'd say, if you're confident in your team as far as their quality as developers goes, then go for Scala. The time lost in learning, will be made up in productivity once they get the hang of Scala and the start experiencing the productivity boost that a more functional approach can give you.