How is your example a language thing? Would a JITed language improve the locality of the m_numLoadedAssets variable? I'm not quite sure I get it.
It depends where *this is allocated. In the worst case, it is allocated in main memory while you wanted to stay in the graphic memory, or something.
A naive compiler would then access memory (or the cache) instead of using registers. A Sufficiently Advanced Compiler would guess that calling ++ many times is the same as incrementing in one go, and hoist that out of the loop, but apparently this one is a bit cruder.
Now the same could be said about m_numAssets, but this one isn't written to, so the compiler only have to put a copy in a register, which I guess is a simpler optimization to do.
To answer your question, that particular situation would be better in any language that forces you to explicit the reference to "this" (or "self"). Imagine how we could modify C++:
void member_function() {
int local_variable++;
local_variable++; // This is okay
member_variable++; // That should not be allowed
this->member_variable++; // This should be written instead
}
void load(Assets* a) {
for (int j=0; j<this->m_numAssets; j++) {
loadAsset(a[j]);
this->m_numLoadedAssets++;
}
}