BnetDocs is down so I can't find it right now, but in C>S theres a Language ID field marked "under research".
I'm not sure what you guys have for leads on it right now, but war3.mpq\config.txt includes this:
// Set the LANGID in [Game] to one of these unquoted constants:
//
// English (US) = 0x00000409
// English (UK) = 0x00000809
// French = 0x0000040c
// German = 0x00000407
// Spanish = 0x0000040a
// Italian = 0x00000410
// Czech = 0x00000405
// Russian = 0x00000419
// Polish = 0x00000415
// Portuguese (Brazilian) = 0x00000416
// Portuguese (Portugal) = 0x00000816
// Turkish = 0x0000041f
// Japanese = 0x00000411
// Korean = 0x00000412
// Chinese (Traditional) = 0x00000404
// Chinese (Simplified) = 0x00000804
// Thai = 0x0000041e
//
// Note: Do NOT quote the constant!
[Game]
LANGID=0x00000409
// Set the LANGID in [Battle.net] to one of these single-quoted strings:
//
// English (US) = 'enUS'
// English (UK) = 'enGB'
// French = 'frFR'
// German = 'deDE'
// Spanish = 'esES'
// Italian = 'itIT'
// Czech = 'csCZ'
// Russian = 'ruRU'
// Polish = 'plPL'
// Portuguese (Brazilian) = 'ptBR'
// Portuguese (Portugal) = 'ptPT'
// Turkish = 'tkTK'
// Japanese = 'jaJA'
// Korean = 'koKR'
// Chinese (Traditional) = 'zhTW'
// Chinese (Simplified) = 'zhCN'
// Thai = 'thTH'
//
// Note: You MUST single-quote the string!
[Battle.net]
LANGID='enUS'
I'm not sure if it's the same thing, but it could be.
They're universally standard language codes. 0x409 = 1033, which is the universal ID for "United States English". I believe the ISO website has a full list, as well. The abbreviations can easily be created using two returns from an API call (I'll post that when I get home).
I figured having this information might be useful to myself in the near future, so I figured I'd go ahead and post this link that I just found.
http://www.krafft.com/scripts/deluxe-calendar/lcid_chart.htm
I'm not sure if this is the entire list, but there's quite a few on there.
Private Declare Function GetUserDefaultLangID Lib "kernel32" () As Long
That's the one. Returns the current Language ID.