You either have to repeat yourself by implementing your data models and validation routines in all the languages your service consumers might use, or instrument some language agnostic way to specify your data models and possibly generate code for them and their validation routines/client libraries, for a myriad of languages.

At that point, your basically reinventing something akin to sql and/or database schemas and constraints without ACID guarantees. You can deploy something like apache thrift or google's protocol buffers, and maybe throw in some swagger.io (which are all great things). But they are yet more layers, that for many levels of scale, increases complexity, rather than reduce it.

Or you can just trust all the services to never have bugs or breaking changes for consumer applications...