There are technologies that solve one problem better than others or for example you already have modules written in Java with all business logic, integrations, security compliance (and what not) and it would take forever to adopt them in another language. Same for Python and ML. Many companies work with different tech stack and for them is also a benefit to have flexibility in that manner.

That mantra is less about using arbitrary programing languages and more about using something like redis (or some other niche/useful/existing tech) instead of recreating the wheel in python/java/node/whatever.

That doesn't require a microservice to do.

If you're breaking an app apart so one part can use redis, you have something seriously wrong in your engineering culture.

You are right of course - my example sucks. I'm trying to think of a more appropriate example, but my heart is not in it.

lol it's all good.