I didn't see any disrespect coming from you; it's just that in a sea of different versions, with someone doing optimisations and another doing fixes, the maintainer has to sort out a lot of stuff to make a version with both fixes and optimisations - and the language barrier does not help.
I have
this repository made so that people can contribute ports to new MIPS platforms to ReGBA under different directories, but use the same common core (and, if improving the core, improve it for all MIPS platforms). The DSTwo doesn't use MIPS32 Release 2 instructions, but the PSP and the GCW Zero do, so the core can work for both. The Japanese person's changes are indeed on top of my optimisations, but they assume the use of PSP extensions to MIPS32 Release 2, which neither the DSTwo nor the GCW Zero can use (!), and he or she made the changes to the core files directly, not to platform files.
On my own, I can't ask for clarifications on what has been done or ask the Japanese person to contribute to my repository.
I find myself in the same situation Exophase faced with gpSP Kai, but I'm not going to actively pursue the developer in Japanese and ask to stop. Instead, I'm going to acknowledge that there's a language barrier and assume that the Japanese person has good intentions and is also language barriered in English.
I also find myself with lots of respect for the merging work done by the VisualBoyAdvance-Merge project folks.