This is the documentation with the original RPC client API specification. The naming convention in the specification is camel case.
Naming conventions might differ in subtle ways for different languages (camel case vs. pascal case), but for some conventions like snake case (Python) or Swift's Fluent Usage API changing the names in the original specification might increase the cognitive load when using the API for those already familiar with the specification.
When searching for different JSON RPC APIs on GitHub, some implementations seem to take advantage of reflection to intercept method calls and pass them to RPC request "as is" so method names for that language are the same as in the original spec. If reflection is not available the names are hardcoded and are mostly the same as the spec, changing only the capitalization of letters for some languages.
Not using Fluent Design in Swift
Not using snake case in Ruby
Changing method names to pascal case in C#