I agree that mixing languages adds complexity. And I say that as someone who routinely does it, because many times it's better to reuse a mature/audited component than rewrite it from scratch.
reply> Mixing C++ with any other language is a huge pain.
replyIt is less pain than for most other languages, except for C. The pain is in exposing a C API for your C++ code. Then you build a library and you're set - because basically every language has the ability to call C code. Python, Rust, Java, etc. etc.
Well once you have a C API, it is relatively easy to call it from any other language.
replyThe painful part is to have to go through a C API (modern languages can express much richer APIs and of course there are different constraints on the different runtimes, e.g. GC).
The annoying part is that each language adds overhead (its runtime). I wouldn't call it painful (I don't have much to do about it), I say "annoying" just because I would rather minimise the amount of code I ship.