About NLS_LANG on Windows Systems
The Oracle client on windows uses a setting in windows to perform local character mapping.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Nls\CodePage\ACP
When the client sends data to the server, the characters are sent in the server's character mapping.
The example NLS_LANG setting above corresponds to an ACP setting of 1252, the default for US Windows. For other languages, consult the Oracle InstantClient documentation to get the correct language, locale, and character map parts of NLX_LANG. Be sure to check the actual ACP setting on your Windows system and make the character mapping part of the setting match it.
The character maps for other languages are as follows. Use them in combination with the correct language and locale to create the NLS_LANG setting.
1250 EE8MSWIN1250
1251 CL8MSWIN1251
1252 WE8MSWIN1252
1253 EL8MSWIN1253
1254 TR8MSWIN1254
1255 IW8MSWIN1255
1256 AR8MSWIN1256
1257 BLT8MSWIN1257
1258 VN8MSWIN1258
874 TH8TISASCII
932 JA16SJIS
936 ZHS16GBK
949 KO16MSWIN949
950 ZHT16MSWIN950