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Why not Algol 68? You can get a modern implementation here: https://jmvdveer.home.xs4all.nl/en.algol-68-genie.html

The documentation for it is great too

And of course there is a VSCode plugin for it as well.

GNU already has an Algol-60 implementation, albeit not as a GCC front-end:

If we're going backwards in time, Algol-W should be on the list (there's a transpiler called "awe", but no actual frontend for gcc/llvm/qbe).