I have not used it myself but colleagues of mine recommend k6: https://k6.io/open-source/

There is also a Github repository keeping track of all the load-testing tools out there: https://github.com/denji/awesome-http-benchmark You will probably find something that will fit your bill.

I do not understand though why it is of any relevance what language the application is written in. Yes, Go and Rust indicate a certain speed and novelty but you can write fast applications with good UX in other programming languages too (and bad ones in Go and Rust).