FlatBuffers libraries are implemented in a big list of languages, as you can see on the website. FlexBuffers is not implemented in all the same languages yet, at least in the official Google repo. Otherwise, it is very relevant in any language--it's a binary serialization format.
If you need a language support for FlexBuffers please create an issue on GitHub repo. I ported it already to Swift, C#, Dart, Python, JS (is in review). If I am familiar with the language you need, it will take me just a couple of days to port it.
