I need to install some version of one package depending on the SO language. How can I get it using a batch file? I'm using W7 professional.
You would need to identify the language codes that you care about. Here is one reference MS Language Codes. Then you could get the code for the current windows install via wmic in your batch file:
wmic path win32_OperatingSystem get OSLanguage
From David's comment, to set the value, use the WMIC /value switch:
for /f "tokens=2 delims==" %%A in ('wmic path win32_OperatingSystem get OSLanguage /Value') do set Language=%%A