Yo!
I only did patch for the EN_US Version, but I guess it's always these 2 char codes (it's a standard i think), but as I can do only sophisticated guesses here I can't really tell you.
One thing i can tell oyu is that if you open Everquest2.exe with a hex editor, you'll see the following at offset 77d91h:
[...]
ZH_TW ZH KO JA FR EN EN_GB DE zh_tw zh_cn ko_kr ja_jp fr_fr en_us en_gb de_de
[...]
I guess this is the country code/version detection, and this sugegsts that EQ2 knows
zh_tw (chinese ? / Taiwan)
zh_cn (chinese ? / china)
ko_kr (Korean / korea) ?
ja_jp (japanese / japan)
fr_fr (french / france)
en_us (english / USA)
en_gb (english / GB)
de_de (german / germany)
So it should always be a <2>_<2> pattern.
BTW. I'm not working for SOE or whatever so this info's could be wrong. I only can say what i see when I look at it.