With iPrint Client 5.68 german localization worked fine.
Ever since upgrading to 5.72 everything is in english.
German nipplibr.dll that ships with 5.72 is dated 07-26-2011, Version 5.6.4.
English nipplibr.dll that ships with 5.72 is dated 10-05-2011, Version 5.7.2.
In fact, all non-english resource-DLLs are Version 5.6.4.
??