It's possible to do manually in all those languages, but I'm not sure it can be done without programmer intervention: C++ and Rust both allow interior pointers/references to point to fields, which inhibits automatic application of many of the craziest layout changes.

I had to add that naively, languages won't do that, because of course there's no trick to it otherwise. Even Javascript can do it, it just won't be any faster. It's a simple example to fit a simple paragraph of text. One could imagine other possible optimizations to harness the fact that it's faster to do work on what you have than to pull more stuff in from RAM, like perhaps a string type that transparently compresses itself with a fixed dictionary (or optional dictionary) or something depending on runtime performance heuristics.

Of course anything I say is possible in an existing language, with enough work, enough assembler, and enough compromises, but it's not what languages are based around.