Tons of great stuff for Unix is written in C++ and other languages all the way to Python and Java. You can write Unix apps in whatever language you want. Ditto for Windows and MacOS.
Not sure what the special deal is with Fuchsia here.
Perhaps you think you'll be able to write Fucshia device drivers with any language you like? That wont be the case at all.
Also Linux has this going in its favor over Fucshia: it actually exists.
