Think of it like this. If you're multilingual but I ask you a hard question with sections in different languages, it's still going to tax you to solve the problem over having the question be asked in one language.

If you codegen client wrappers from your specs that can help, but if something doesn't work predictably the indirection makes debugging harder (both just from a "cognitive" standpoint and from inability to directly debug a unified system).

I prefer FaaS + shared libraries over microservices when I have to part things out, because it gives you the independence and isolation of microservices, but you're still sharing code across teams and working with a unified stack.