Or, put it another way, a html renderer that can open most web pages, but has a different programming/scripting language that it can interpret during runtime or on page loads, instead of the javascript engine.
I suppose that java applets, flash and activeX were attempts in these directions, but they were things you had to install on top of the browsers, so not quite the same thing? I’m imagining something like web pages using Lua, since it’s lightweight, to make them dynamic.
If you want lightweight it’s probably better to stick with js or some language that compiles directly to wasm.
That’s being said, there are libraries for running python/lua/ruby in a browser and interacting with the dom. I’ve only personally used python, which is great for running scientific computation things in browser since python has such an ecosystem for that type of thing. It is a pretty big addition to bundle size initially iirc, so I’m not sure how useful it is as a general purpose replacement for js.
Python Lua Ruby
Opal also compiles Ruby to JavaScript https://opalrb.com/