It would seem that the requirement for multiple languages often has nothing to do with making something or the customer requirements. It's often a developer requirement. Developers want to work in their favorite language. In the 90s you just wrote in whatever the company or ecosystem had mandated. Now that developers are in high demand they can specify what they want to use.

It started with books like "Beyond java" (and java was beyond C++) and disparaging articles by the likes of Paul Graham. They made some good points but if you have ever worked on a single system with multiple languages and are honest about it you would have to say that it wastes an enormous amount of time and generates unnecessary complexity. When a developer has to make a microservice just to write part of the system in another language you have wonder if they have the ability to evaluate technical trade-offs. Just pick one language and get on with it.