The TIOBE Index (of programming language popularity) for April 2015 notes that:
Another interesting move this month concerns Scala. The functional programming language jumps to position 25 after having been between position 30 and 50 for many years. Scala seems to be ready to enter the top 20 for the first time in history.
Scala is the language in which the hugely popular Apache Spark large-scale data processing engine is written—which, no doubt, explains the sudden burst of enthusiasm for the language.