How to know SQL Server installation language while it is down?
You can check the system registry to determine the installed language for SQL Server.  To get the name of the SQL Server Instance Key, first look at this registry key:


  HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\Instance Names\SQL


That key shows a list of installed instances; the Data column shows the registry key name to use when looking for the Language key in this key:


  HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\&lt;name-from-previous-step&gt;\MSSQLServer\CurrentVersion\Language


This Microsoft site lists the various language IDs and the corresponding language name.

I wrote a quick blog post showing this process in greater detail at SQLServerScience.com.