(medium-sized project, that is)
It turned out to be a small-sized project in Smalltalk. Including unit tests and refactoring :)
I still do not think C++ is "anything but a mess". It's usable. Smalltalk (and Python, and TCL to a lesser degree) are joy to code in. But I still don't trust them for critical loop stuff. And that's where I spend a lot of time, myself. From that point on, it's a matter of investing into some coupling, or continuing with C++ all the way up.
(Side note on unit tests: I realized that in Smalltalk, unit tests cover a lot of stuf that compiler checks in C. So, in C I write unit tests to verify control logic, and in Smalltalk I write them for every line of code indeed.)