function GetTranslatorNameAndEmail:widestring;

These two lines do the same thing:

LabelTranslator.Caption:=DefaultInstance.GetTranslationProperty('Last-Translator');
LabelTranslator.Caption:=DefaultInstance.GetTranslatorNameAndEmail;

In other words, this function is just an easy way to fetch the translator name, but not the only one. See the Section called function GetTranslationProperty (Propertyname:string):WideString;> for more information.