Oh, like a Lisp machine. ;)
(Be careful what you wish for, though; the 'one language to rule them all' world was essentially why ADVENT was written in FORTRAN of all languages.)
(Also: Was it ever just one language? Eight-bit systems always had BASIC and assembly language; for a lot of tasks, assembly language was pretty much it, unless you bought a Pascal compiler or something. Lisp machines had Lisp written in the normal way, Lisp written in an obscure way to improve performance, and microcode. Even old AS/400 systems had COBOL and RPG, which is rather a pick-your-poison dilemma but the choice was there.)
lanuages_onboard="lua" -- .. &etc.