What percentage of microservice architectures employ polyglot programming models?
A good source for statistics could be stackshare.io.

In general, polyglot services i.e. teams delivering different stacks could create silos, and additional overhead for diverse toolchains; nevertheless I consider that larger organizations have the polyglot situation organically because this type of thing is not always an issue of top-management. 

Arguments against polyglot approach:
"Why You Should Think Twice Before Even Considering Polyglot Microservices"

Worth to mention is the polyglot toolkit Eclipse vert.x (though I am not sure how is this different to say "it has bindings to many languages").