>You might be looking for a specialist but you don’t want to attract people who are only interested in particular languages. Because that person’s narrow focus will hinder their growth.
Exactly what I have been witness to was this taken to the test. Result:
* You hire devs who do not like (or worse: hate) working in the language of the shop. They scold at the application they have to maintain and run, they do not contribute libraries or fixes, and topic number 0 at all larger meetings is "how we should rewrite everything in TypeScript/Go/Kotlin/whatever-tech-the-freshly-hired-senior-person-likes-best"
* You hire devs who do not care about the ecosystem. When the time comes to fix an external dependency which is not up to snuff, they will be saying things like "well if this app was written in $my_favourite_lang instead, this would have been so much easier"
* You create an infighting culture between people who do like to work with the current setup and people who want to destroy it and replace it with their favourite setup, be it for language preference or for "getting promoted" reasons
Briefly: no, I think it is absolutely imperative - especially at a company which is not polyglot - that even if it is not a requirement to be super-proficient in the main tech at the shop, it must be a requirement - and not a soft requirement - that the eng. be prepared to work, explore and develop in that tech. If this requirement is not present or not met, you are setting up your company for turf wars potentially for years to come.