When using the german locale, s:textbox (and supposedly also other tags) don't use localization for Double values. Effect: in a form that prints a double value to a s:textfield with value="doubleVarName", the double value of 1.0 is printed out while it should be 1,0 with german locale. If the same form is sent to an action, the params interceptor interprets the 1.0 somehow differently and stores 10.0 in the double field "doubleVarName".
I don't find another hack for me other than forcing english locale, which is okay for my app but might not be okay for other developers. (My first bugreport, hope it's fine)