In Rust you have the amazing serde with serde_json but at this point, you can use toml which is also based on serde. I consider serde as being standard.
In C you have the lib jason which is very good.
In Elixir, I use the compile-time configuration (config/config.exs) with environment variables for production, but that's because in the end, my Elixir system is in a Docker container, running on Kubernetes, with a ConfigMap defining the environment variables, so in the end, it's YAML (or JSON).
In Rust you have the amazing serde with serde_json but at this point, you can use toml which is also based on serde. I consider serde as being standard.
In C you have the lib jason which is very good.
In Elixir, I use the compile-time configuration (config/config.exs) with environment variables for production, but that's because in the end, my Elixir system is in a Docker container, running on Kubernetes, with a ConfigMap defining the environment variables, so in the end, it's YAML (or JSON).