Let me ask you this: imagine a group of programmers who you work with now or have worked with in the past. Now imagine they all worked for you in a company that you personally owned. Would you require them to try out a new language every year and pay them to do it? Do you think it's that important? Might it be true that some of your programmers would benefit more from using that time to learn something else?
I'm not sure that it's the right question to ask. What I would do is irrelevant.
Everyone has different sets of skills that make them individuals. With every new experience, we shape our vision of what we do.
I did some hiring in the past, and I might have hired someone because (as additional "talents") they were funny, because they liked board games, or because they liked reading.
People in my team have asked for training of many different kinds, spanning from computer languages to design, to communication skills. To this day, I've done my best to say yes whenever I could. I have also let them dedicate some of their time to whatever they liked. Not because I thought that they would, in a day, dramatically improve at programming, but because they would enjoy it and that in the end, it would benefit the company (and my team). To me, the key is to let people decide, and if they feel like learning a new language, I'm okay with it.
Now, let's focus back on languages. In my current company, we mainly use Java and PHP, but ... someone saved the day when he was able to tweak the swagger code generator (written in Scala), someone was able to save the day thanks to her go skills when she quickly wrote a program with parallel tasks, someone was able to save the day when he configured Jenkins using Groovy, someone debugged a PHP extension (written in C), and someone just had fun with colleagues showing them a game prototyped with Unity.
Are they "better" programmer? No.
Was it useful for the company? Yes.
Would I hire them "because they know five additional languages?" ? No.
They just happen to have developed an appealing amount of knowledge and skills, sometimes by learning a new language.
Yeah, I totally agree. And thanks for treating your programmers as humans; I'm sure they appreciate it.
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