What can be used to write a cross-platform data converter?

Question

Cross-platform

I need something like a console application that communicates over TCP / IP (probably the most suitable one). The whole point of it is data conversion (so as not to write your own converter for each platform), for example Input : "123qwerty" ; Output : "ytrewq6". It does not need a UI at all, even in the form of a console. Suggested platforms android and windows. The language is not important, I do not want a lot of trouble with installation and configuration. I looked at flutter and it seems to be for UI, where I saw that it is possible on node.js and I will also try on kivy. Can you recommend something better?

Answer 1

Someone invented Apache Airflow, which runs on top of Apache Kafka, which just works over tcp.

Answer 2

Take Java or Kotlin, because only on them you have full control over the life cycle of an android application.
Java also works on Windows.
But you still have to write a lot of specific code on both platforms.