Anecdotally, it does somewhat fine with C++ and OpenCV. Python is great, though PySide much less so. QML is almost useless. GLSL is OK, but not great. It generally can't reason well across language barriers, although it's great at converting between languages.
The deeper into a nerdy domain I go, the less likely it is to understand what's going on. And more broadly, it seems that usefulness steeply declines for larger files and projects. It just can't fit enough context into its window to make sense of complicated things.
As an extreme example, I told it to average two angles, and it just took the mean of them. Even after prompting, it thought nothing wrong of that. (The average of 1° and 359° is 0°, not 180°.) So it goes for many domains outside of webdev, UI, data science, scripting.
Even Python gets a bit touchy if you ask it to avoid common packages.
An example is asking for simple Kalman filter, limiting to 2x2 matrix to avoid the need for LU decomposition. If you ad to the prompt a constraint to not use Numpy, which almost everything in the corpus does.
Even with LRM's having a high enough top-k accuracy, so that at least one correct solution given in k guesses seems to be the trick.
Perhaps Pyhon+Numpy is a language barrier but the errors without Numpy seem really trivial, similar to what one would see on an obscure language. It is different across different models, but getting stuck generating verification code with divide by zero to giving up and producing code that uses numpy are failure modes I have seen.
Professor Subbarao Kambhampati's explanation really helps here IMHO.
"Compiling the signal verifier" in, at least superficially to me, is a good intuition on where these fail.
The limits of Top-K and heavy tail dependance in many tasks will be something painful, I think we will need more expertise and not less among programers just due to the failings of us humans and our over trust of automation etc...
How we change the career path to develop tacit and technical abilities is a big question personally.
The internet is full of javascript/html/css info. Some wrong some obsolete some right and current, but there is data.
How about the more peasant languages?