Gui: Improve localization support in VarSet dialog (#17480)

* Gui: Improve localization support in VarSet dialog

* Gui: Adopt QObject translate

This is not the ideal implementation but for the 1.0 release this is
currently the better option.  A separate issue has been filed for post
1.0 in https://github.com/FreeCAD/FreeCAD/issues/17510 that also covers
the `DlgAddProperty`.

src/Gui/DlgAddPropertyVarSet.cpp

@@ -174,9 +174,7 @@ void DlgAddPropertyVarSet::initializeWidgets(ViewProviderVarSet* viewProvider)
     connLineEditNameTextChanged = connect(ui->lineEditName, &QLineEdit::textChanged,
             this, &DlgAddPropertyVarSet::onNamePropertyChanged);
 
-    std::string title = "Add a property to " + varSet->getFullName();
-    setWindowTitle(QString::fromStdString(title));
-
+    setTitle();
     setOkEnabled(false);
 
     ui->lineEditName->setFocus();
@@ -188,6 +186,11 @@ void DlgAddPropertyVarSet::initializeWidgets(ViewProviderVarSet* viewProvider)
     // printFocusChain(ui->lineEditName);
 }
 
+void DlgAddPropertyVarSet::setTitle()
+{
+    setWindowTitle(QObject::tr("Add a property to %1").arg(QString::fromStdString(varSet->getFullName())));
+}
+
 void DlgAddPropertyVarSet::setOkEnabled(bool enabled)
 {
     QPushButton *okButton = ui->buttonBox->button(QDialogButtonBox::Ok);
@@ -219,6 +222,15 @@ void DlgAddPropertyVarSet::removeEditor()
     }
 }
 
+void DlgAddPropertyVarSet::changeEvent(QEvent* e)
+{
+    if (e->type() == QEvent::LanguageChange) {
+        ui->retranslateUi(this);
+        setTitle();
+    }
+    QDialog::changeEvent(e);
+}
+
 static PropertyEditor::PropertyItem *createPropertyItem(App::Property *prop)
 {
     const char *editor = prop->getEditorName();

src/Gui/DlgAddPropertyVarSet.h

@@ -74,6 +74,7 @@ public:
     DlgAddPropertyVarSet(QWidget *parent, ViewProviderVarSet* viewProvider);
     ~DlgAddPropertyVarSet() override;
 
+    void changeEvent(QEvent* e) override;
     void accept() override;
     void reject() override;
 
@@ -85,6 +86,7 @@ private:
     void initializeTypes();
     void initializeWidgets(ViewProviderVarSet* viewProvider);
 
+    void setTitle();
     void setOkEnabled(bool enabled);
     void clearEditors(bool clearName = true);
     void clearCurrentProperty();