If we accept this definition, C++ already seems to be many different languages. At my job, I'm currently fighting floating-point determinism issues across different build configurations, compilers, CPUs, operating systems, and standard library and libm implementations so that snapshot tests pass with the same hashes on all platforms. I can confirm that this is a complete nightmare.

Yup. I tried hard to not allow D's behaviors to be changed based on a compiler switch. Yes, we have switches to enable certain features, but not silent behavior changes.

It's not perfect, but the forest of such switches in C compilers motivated D to not have them.