> So where are the examples of that being done?
Whenever people want to get valuable information. As I said, we in OpenJDK have a couple hundred benchmarks, some macro, many micro, which are meant to give a decent coverage of the things that affect performance.
If a website wants to group results by languages, it should think about performance from the perspective of how languages work (which include compilers, linkers, and runtimes).
For example, what compiler/linker optimisations are done can depend a lot on whether the program is in a single compilation unit or multiple (and in the case of C and C++ - it does).
On the runtime front, think about memory management. These mechanisms often have different behaviour depending on whether the objects are of similar size or not, whether they're allocated and freed by multiple threads or a single one, and whether the heap is "young" and unfragmented or old and fragmented.
Another area in runtimes is data structures. Are they single-threaded or concurrent, and if concurrent, how do they behave under low and high contention?
Some mechanisms, in all of these levels, have great performance under some conditions and not so great performance in others, and sometimes where they perform great is actually a condition that is encountered less often in real programs.
If you're asking what multi-lingual benchmark suites offer good coverage - I don't know. But that we don't have good information doesn't mean that it's good to offer bad information. Imagine that in American presidential elections there were no national polls and no polls in most states. Would having a poll only in Alabama or only in California offer good insight into who's likely to win? Probably not, because such a poll offers a very partial view of the situation. Is it better than nothing? Maybe, but not by much, because the outcome in Alabama and California is easy to predict without any polls, so it's only helpful in the most extreme cases.
My point is that bad information is bad information, and if people don't understand how different languages behave under different conditions (e.g. that the optimisations the compiler does can differ depending on whether the program is in a single file or not) then they can get the wrong impression. Imagine that someone has no idea about the regional polarisation in the US, and you tell them, well, there are 50 states, but since we don't have polls for all of them, here's the poll for Alabama. Is that information helpful at all?
In any event, any increase in the coverage makes the information a little better, and because the audience may not know whether multiple benchmarks exercise the same or different behaviour in the language, it's the role of the website to pick problems that trigger the different codepaths in the languages' infrastructure. Otherwise, there's the wrong impression of variety, like saying we don't poll only in Alabama but also in Mississippi. Or it's like testing the structure of a bridge by driving a car across it, and then doing it with ten different car models. Testing a bridge does require variety, but the different car models are not what triggers different conditions for the bridge.