I'm curious as to how GameEX has such information on each ROM. This is something I've always wanted to do/add in romlister too (well, at least be able to filter non English titles anyway) but there is nothing in MAME's -listxml that has regional or language information in it, other than removing anything that has the keyword Japan in it, or perhaps a certain manufacturer.
If there's another controls.dat or catver.ini or similar datafile which has information like that, I will *gladly* change my code around and add support to pull in that info too.
-jeff!