Some of your questions are answered in the link I gave you in your other topic, some are not. Here's a quick recap tho'.
"...do you have to hook up extra wires to get stereo sound?"
Yes and no. If you have a US, Hyper board, there is extra wiring. If you have the newer, Japan released only board, the JAMMA connection gives you stereo (I currently have my Jp board in an MVS, stereo cab hooked up with nithing but JAMMA and get stereo).
"Also,if you have a Japanese system can you change the language to English...?"
Yes you can. However, in order to do so, you need to have a button hooked up to JAMMA pin 15 of the board. When pressed, this puts the Hyper board into "Test" mode, where the software dips can be fiddled with, one of the options being language. I have not yet bothered to hook up a switch for mine.
For more detail on the boards, I would still suggest checking the link I posted in your other topic. <IMG SRC="smilies/biggrin.gif" border="0">