We have static #programming languages that are both adequate for the server-side and can target the client-side (Javascript, WASM, native, etc), such as #Scala, #Kotlin, #Rust, #FSharp, #Typescript.
The biggest advantage of using the same language is that you can share code, starting with the data models, alongside serialization, and parsing/validation rules. The API can thus be easily kept in sync, and a server-side test is also relevant on the client-side.
