Perhaps instead of any actual programming language you could use the pseudocode[1] used in scientific (comp-sci) papers. It should be understandable for longer than any current language.
I suspect that would last longer, the issue is that it'd be harder for someone to practically use it because they'd need to pay a programmer to implement the algorithm for them -- while if we embedded a Python script (for instance) they would just need to ask a technically-literate person to show them how to run it.
Though I suspect JavaScript would last the longest given how much internet culture has been written in JavaScript (and so long as projects like Archive.org exist, it should be possible to run JavaScript).
Ultimately doing both is probably better than one or the other.
Ultimately doing both is probably better than one or the other.