The onlinehelp in German regarding ZN(expression) is misleading
in the original English version it is clear, ZN means something like "zero if NULL"
But in the German translation zero and NULL are both translated as "Null"
Formally this correct, because the are no different words in German, but in this database context this needs to be changed or explaned. You could translate
ZN - Zero if NULL
Gibt den Ausdruck zurück, sofern er nicht NULL (NULL) ist; anderenfalls wird der Wert Null (0) zurückgegeben. Nutzen Sie diese Funktion, um den Wert Null (0) zu verwenden anstelle von NULL (NULL)-Werten.
Maybe you should also do this on other places in the translation.
BTW, it would be fine to have an option, if Tableau could be used in German but the help language could be switched between local language and original. Or it would be fine if in the online help in the web there would be a quick link to the original. Than in case of unclear translation the original site could be opened quickly.