Controlling the encoding of ID3v1 tags?

Some of my songs have titles and artist names in Japanese. Japanese text works perfectly with ID3v2.3, but I would also like to have correct Japanese Shift-JIS text in ID3v1 because the music player on my Nintendo 3DS ignores ID3v2 tags in certain cases but supports Shift-JIS in ID3v1. ID3v1 tags are normally saved as Windows-1252 (or is it ISO-8859-1?), which doesn't contain any Japanese characters, so the entire text just gets replaced with question marks. In the past (using older versions of Mp3tag – I haven't tested this on the newest version yet), I have noticed that Mp3tag will save ID3v1 tags as Shift-JIS if I change the Windows system language to Japanese. That does exactly what I want, but having to change the system language and restart my computer every time I want to tag something in Japanese is a hassle. Is there any way to change the ID3v1 encoding without having to restart my computer, like a setting inside Mp3tag? I haven't been able to find one.

The character set for ID3V1 is not specified and may be saved as sind ASCII, ISO 8859-1 and Unicode, encoded as UTF-8. So you will get those problems that you noticed.

And no, you would have to change the OS character set/code page to get the right characters.

What I don't understand is the strange restriction that a program should read a tag sometimes and sometimes it does not... could it be that something else is wrong with these files, e.g. an APE tag somewhere in the files or a corrupt header or something?

Indeed.

Okay. That's unfortunate, but thank you for the information.

From what I've seen, it always fails to read tags that are bigger than roughly 500 or 512 KiB. High-quality album art pushes my tags over that limit sometimes. I prefer to keep the album art large so it looks nice on other devices, even though it makes the 3DS music player fall back to ID3v1, because that music player doesn't support ID3v2 features like album art anyway.