The "historical anecdote" is that somewhen around kernel 0.99, C++ was tried. And given up due to both compiler bugs and (worse) abysmal compilation performance.

For all I know about Ada, the latter has a reputation for "non-speed" on compile worse than C++ even. Nevermind that gnats (gcc ada integration) post-dates Linux by a few years.

Of course, it could simply be that Linus looked, got an allergic fit, and hence didn't bother ...