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.
You could transpile different languages into JS. So you write in the language of your choice, transpile it to JS, then send the transpiled JS to the user’s browser. You could possibly do the same thing but use webasm as well.