Yes.
Yes, DS games are not region locked.
DS games are not region locked, you can play a Japanese DS game on a US DSi. DSi store access is allocated by region though, so some DSiware might not be available.
Yes, since Nintendo DS games are not region locked, the Japanese DSi can play North American games. The Japanese DSi is not physically different than the North American DSi so accessories will work as well.
Yes. DS games are not region locked.
no. Nintendo dsi are region locked. that means that if you buy a Japanese dsi then it only works with Japanese games
no you can't play dsi games in ds but you can play ds games in dsi.
YES!
No. The DSi is region locked.
The DSi can play DS and DSi games, as well as DSi ware games. It cannot play GameBoy games or 3DS games.
On the Nintendo DS you can play any game without region lock so that means you can play a japanese DS game on an american DS but on the DSi and on the 3DS there is a region lock which means you can only play games that compatible with your DSi/3DS region. NTSC (=american) DSi/3DS can only play NTSC games, PAL (=european) DSi/3DS can only play PAL games and NTSC-J (=japanese) DSi/3DS can only play NTSC-J games.
Yes, you can play DS lite games on the DSi as well as the DSi XL
The DSi XL is not region locked, it will play games from any region. The exception is for games marked as 'DSi-enhanced' such as Pokemon Conquest. These work in a regular DS or 3DS, but not a DSi from the wrong region.