I'm trying to reach a japanese path. Something like "C:\日本語\asd.dll", but I have some problems. If I force my installer to put the dll file to C:\Windows\System32, will that path be the same in all language versions of Windows or it will be in the regional language?
No, you cannot in general rely on paths being the same. Always use the environment variables - you can guarantee that the environment variable names will not be localized (i.e. "%SystemRoot%" works everywhere). In your example, you would want to put the file in %SystemRoot%\System32
.
Though, I would advise to not be putting DLLs in this directory, as it belongs to the OS.