The popular NUSB drivers for Windows 98 SE, which enable native USB mass storage support, are tailored to specific language releases of the OS. The English one (ending with ‘e‘, like nusb31e.exe, nusb33e.exe or nusb36e.exe) is the most common. Some of the different language versions are offered here, but there are more localized/enabled releases of Windows 98 SE than there are versions of NUSB out there.
Installing the wrong version for your language will most likely render your system non-functional (you will be greeted with a blue screen as soon as Windows is loaded). This is because NUSB replaces some system files in WINDOWS\SYSTEM, with incompatible versions (as they are taken from a different language release). Fortunately, the fix is simple – the files are SYSTRAY.EXE, USER.EXE and USER32.DLL. All you need to do is restore them from the original Win98 SE installation CD. An easier way is to back them up before installing NUSB, then restore them. To do so, if Windows fails to load, simply boot to “Command Prompt Only” mode, and restore the files from the backup location to WINDOWS\SYSTEM.
I could confirm that the USB mass storage support is still functional after restoring the original files. I am not sure why NUSB even touches them, but it may be that the modified files provide some additional, though not critical, functionality.