I think you can solve the Run Time Package problem by switching your computer entirely to Japanese locale and then switching back to English after installing it. I'm not sure for Windows 10, but for other operating systems, this won't change everything into Japanese, all the text on the computer will stay in English. However, some programs like Skype and McAfee will switch their interfaces to Japanese.
Also, RPG Maker, especially the 2000/2003 versions, has no means of optimization, so the developers have no way to make it fully compatible with newer OSs, unless the developers of RPG Maker update the Japanese version of 2000/2003, which seems unlikely.