Or Forth with scientific library, bound to the constraints. Put some HTTP library on top and some easy HTML interface from a browser with no JS/CSS3 support at all. It will look rusty but unexploitable.

Enterprise computing with custom software will make a comeback to avoid these pitfalls. I depise OpenJDK/Mono because of patents but at least they come with complete defaults and a 'normal' install it's more than enough to ship a workable application for almost every OS. Ah, well, smartphones. Serious work is never done with these tools, even with high end tables. Maybe commercials/salespeople and that's it.

It's either that... or promoting reproducible environment with Guix everywhere. Your own Guix container, isolated, importing Pip/CPAN/CTAN/NPM/OPAM and who knows else into a manifest file and ready to ship anywhere, either as a Guix package, a Docker container (Guix can do that), a single DEB/RPM, an AppImage ready to launch on any modern GNU/Linux with a desktop and a lot more.