I don't think "avoid otherwise-unused languages for secondary tools" is the same as "avoid less common languages for your main product". Every software developer at your company will likely work on your main product for a non-trivial amount of time. Any software developer who can't figure out a new language in a trivial amount of time isn't worth hiring. Thus, everyone you hire will eventually be competent in the language of your main product.
In contrast, for secondary products, there's a good chance most developers will never work on it at all, and of those who do a significant fraction will spend only a trivial amount of time. Adding the overhead of working in a new language to that balance is significant.
Therefore, the ideal is "Choose the best language for your main product, then write all supporting software either in that language, or a widely-used lingua franca like Python".
In contrast, for secondary products, there's a good chance most developers will never work on it at all, and of those who do a significant fraction will spend only a trivial amount of time. Adding the overhead of working in a new language to that balance is significant.
Therefore, the ideal is "Choose the best language for your main product, then write all supporting software either in that language, or a widely-used lingua franca like Python".