I have heard arguments over the years along the lines of this:
We need to use programming language X because developers proficient in this language are easier to recruit.
Developers deserve a lot more credit than that. Most developers can pick up new programming languages reasonably quickly, especially languages in the same general category used together. For example, few Java business application developers cannot know SQL, and few front-end JavaScript engineers can get away with not knowing CSS.
I was, presumably, a Java developer for roughly 18 years of my career before 2015. At a minimum, I used Java and SQL for my work, which was considered an essential requirement. I used UNIX shell scripts for automation. If I ever restricted myself to being exclusively a Java developer, I had to know at least 3 programming languages just to get my work done.
I believe that pigeonholing myself into a single programming language or a single platform would have been detrimental to my career, and I am glad I never fell into that trap. Where are, may I ask, all the Deplhi developers?
Perhaps, we shouldn’t be recruiting developers based on some single technology they know but on what they can learn and apply in the future. A generalist developer that can pick the right tool for a given taskand articulate why they made such a decision is a lot more valuable than a specialist.
The Dulin Report 