Also check if by any chance you haven't got a file "icui18n56.dll" elsewhere (in particular somewhere in c:\Windows).
Some automatic software update may have replaced/add another version of the file, in a place that takes precedence over the one that comes with Gimp (or your plugins)
Some automatic software update may have replaced/add another version of the file, in a place that takes precedence over the one that comes with Gimp (or your plugins)