You cheated ;-)
In the tutorial, you create two separate properties files;
StockWatcherConstants_de.properties and
StockWatcherMessages_de.properties
But you have only created StockWatcherConstants_de.properties,
and in there you put both your static and generalized strings.
Try creating a StockWatcherMessages_de.properties aswell and put these
rows in there:
lastUpdate = Letzte Aktualisierung: {0,date,medium} {0,time,medium}
invalidSymbol = ''{0}'' ist kein gültiges Aktiensymbol.
and remove the same rows from StockWatcherConstants_de.properties
> gwt-SW-src.zip
> 11KVisaHämta